Laser ablation spectrometry apparatus

ABSTRACT

Apparatus for laser induced ablation spectroscopy (LIBS) is disclosed. An apparatus can have a computer, a pulsed laser and a lightguide fiber bundle that is subdivided into branches. One branch can convey a first portion of the light to a first optical spectrometer and a different branch can convey a second portion of the light to another optical spectrometer. The first spectrometer can be relatively wideband to analyze a relative wide spectral segment and the other spectrometer can be high dispersion to measure minor concentrations. The apparatus can further comprise an unbranched lightguide fiber bundle to provide more light to a low sensitivity spectrometer. The apparatus can include an inductively coupled plasma mass spectrometer ICP-MS and a computer instructions operable to provide normalized LIBS/ICP-MS composition analyses.

FIELD OF THE INVENTION

The present disclosure relates generally to the art of chemicalanalysis, and more particularly relates to improved apparatus andmethods for monitoring the composition of a solid and liquid samplesusing spectroscopies based on laser induced ablation.

BACKGROUND

Elemental composition analysis is essential to determine the safety andquality of products in various industries including petroleum,cosmetics, metallurgy, recycling, mining, pharmaceutical, medical, foodindustry, and others. However, very few low cost, rapid, reliable, andpractical instruments and methods are available to perform elementalcomposition analysis of samples depending on the requirements andstandards of an industry and/or characteristics of samples.

Restriction of hazardous substances by statutes such as the Directive onthe Restriction of the Use of Certain Hazardous Substances in Electricaland Electronic Equipment 2002/95/EC (commonly referred to as theRestriction of Hazardous Substances Directive or RoHS) was adopted inFebruary 2003 by the European Union. The state of California has passeda similar law. The directive restricts the use of six hazardousmaterials in the manufacture of various types of electronic andelectrical equipment. The six hazardous materials include Lead (Pb),Mercury (Hg), Cadmium (Cd), Hexavalent chromium (Cr-VI or Cr6+),Polybrominated biphenyls (PBB), and Polybrominated diphenyl ether(PBDE).

Industry seeks efficient and economical measures to comply with RoHS.Dissolution in acid is commonly used to test and measure compositionalqualities of sample material. This method has inherent disadvantages.Laser induced breakdown optical emission spectroscopy (LIBS) as well asother laser spectrometry methods are potentially efficient andeconomical techniques to determining and/or verify the composition ofproducts and other materials.

Analyses using prior art LIBS has often shown excessive variability. Amajor source of this variability has been inconsistent plasma plumegeneration by the pulse laser. Former LIBS type analyses have often beenunsuccessful in matching known standards achieved with other analysismethods.

Traditional chemical analysis has traditionally been based on variousstandard methods in which each method was suitable for, or sufficientlysensitive to measure only a relatively small number of elements. Generalmulti-element analysis providing sub-ppm (sub-part-per-million)detection limits for metals can be performed using inductively coupledplasma-optical emission spectrometry (ICP-OES) based ultravioletspectral region. However, this ICP-OES requires complex samplepreparation including acid digestion of samples, as well assophisticated equipment, fast flow of high-purity argon,quartz/glassware and expensive consumables. The process generateshazardous chemical waste that must be disposed after an ICP measurement.Lengthy sample handling, high power requirements (˜3 kW) and largeequipment dimensions have impeded the use of ICP-OES for rapid fieldmeasurement of species found in petroleum sources. ICP operation has notbeen adaptable to be performed outside of a laboratory environment.

In principle, LIBS should be applicable to analyze solid/or liquid,phase material. A commercial LIBS instrument operable to reliablyanalyze liquids could improve refinery manufacturing by eliminating lagtimes and improving accuracy in process control and optimization sinceit can determine both major and minor and trace elements such as occurin petroleum fractions and fuels. With regard to an important need forfuels, LIBS has particular sensitivity to detect and quantify lightelements and halogens (e.g. Hydrogen (H), Lithium (Li), Beryllium (Be),Boron (B), Carbon (C), Oxygen (O), Nitrogen (N), Fluorine (F), andChlorine (Cl) which are difficult or impossible to measure withsufficient sensitivity using conventional and/or more costlyinstrumental techniques such as ICP. However, with regard to commercialinstruments useful for industrial applications, LIBS has only beenuseful for solid sample analysis despite prior art attempts to developpractical apparatus and methods for liquid phase elemental analysisusing LIBS.

The composition of petroleum feedstock, particularly metals content, isa critical factor in deciding how a specific lot of crude oil is usedand the specific refining requirements. Various crude oils have verydifferent composition, and these differences critically affect therefining methods that are used to produce fuels and other petroleum andpetrochemical products. Crude petroleum contains traces of inorganicsalts, nitrogen, oxygen, sulfur, halogens and metals. For example,vanadium (V), nickel (Ni), iron (Fe), and sodium (Na) are often majormetallic constituents of crude oil. Other metals can be unintentionallyintroduced during production, transportation and storage. As well,halide impurities such as salts, when present, can hydrolyze to formhighly corrosive acids. Even trace amounts of such elements can impairrefining. Refineries may purchase crude oil daily or hourly. An improvedability and speed for detecting these elements at a part-per-million(ppm) sensitivity level using LIBS could improve refinery efficiency andthe ability to provide higher quality refinery products.

As well, various contaminants in gasoline must be precisely known sinceexcessive amounts can foul fuel injectors in vehicles and/or deactivatecatalytic converters. Fuel analysis must be performed with sub-ppmsensitivity for Copper (Cu), Cadmium (Cd), Zinc (Zn), Iron (Fe), Cobalt(Co), Nickel (Ni), Lead (Pb) and other heavy metals. For example, morethan 0.05 ppm of Cu is likely to impair fuel thermal stability.

LIBS analysis of liquid phase samples has been difficult for a number ofreasons. Depending somewhat on the sample liquid volatility and surfacetension, liquids can adhere to, coat, and/or form droplets attaching tooptical and/or other elements of the apparatus. Liquid analysis usingLIBS requires a liquid to be rapidly vaporized using one or more laserpulses. However rapid vaporization inherently results in the formationof droplets and/or splashing, depending on the form and confinement ofthe liquid during the vaporization process. Liquid or liquid dropletsreaching optical elements, or liquid vapor condensate on opticalelements, can scatter light, disturb optical alignment, transmission,and/or other aspects of light gathering, thereby interfering with lightgathering and/or degrading analytical sensitivity and stability. Thesephenomena have required frequent operator intervention to clean andrestore operability of prior art LIBS equipment, making sustainedoperation difficult and/or impossible. For at least the above reasons,no LIBS instruments and/or methods for analysis of liquid samples havefound commercially success.

There has been a long felt need for a single analytical instrumentcapable of providing rapid and sensitive elemental analysis of bothmajor and trace amounts of light and heavy elements in liquid and solidsamples. More particularly, there has been a need for a single, readilytransportable analytical instrument with these capabilities in thepetroleum, aviation, semiconductor, metallurgy, recycling, mining,pharmaceutical, medical, and food industries. As outlined above, LIBStechniques can provide temporally and spatially resolved analyses of thenecessary light and heavy elements. Since a high-power laser source,power supplies, controls systems, optical spectrometers, and specializeddetectors used for LIBS are relatively costly, it is apparent that asingle instrument capable of analyzing both solid and liquid samples cansave cost and relatively enhanced transportability. However, prior artattempts to provide methods and apparatus operable to perform reliable,low maintenance, real-time, automated analysis, of liquids with LIBS,and/or of solid and liquid samples using common components based on asingle instrument have been unsuccessful.

SUMMARY

In a first aspect of the present disclosure, a laser ablationspectroscopy apparatus is provided. A pulsed laser is focused on asample site to generate a plasma plume during a laser ablation process.The plasma plume can be detected with an optical spectrometer having anintensified charge coupled device. A sample of material is coupled to astage movable in independent x, y and z directions using an array ofx-y-z motors. A change in the height of the sample is detected using asensor. Preferably, the sensor is a triangulation sensor. The apparatusincludes a system computer for synchronizing the movement of the stagein the x, y and z direction during the laser ablation process. Theheight of the sample site can be automatically adjusted following eachlaser ablation. In one embodiment, the system computer includes acontroller, application software and a graphical user interface (GUI).

In another aspect of the present disclosure, a method of laser ablationspectroscopy is provided. The method includes a protocol of generatingone or more laser ablations to a sample site. The spectral data of theindividual laser ablation sites can be used to form a chemical map ofthe sample surface or the total number of laser ablations for the sitescan be averaged together. In some embodiments, the total number of laserablations for a sample site equals three laser ablations. The protocolincludes laser ablating additional sample sites and averaging thespectral data of the total number of sample sites. In some embodiments,there can be more than 30,000 sample sites.

An innovative aspect of the subject matter described in this disclosureis an implementation of a laser induced breakdown spectroscopy apparatusfor liquid and solid samples that provide quantitative data with highaccuracy, sensitivity and reproducibility. Furthermore, the disclosedLIBS apparatus can be designed as a compact and portable singleinstrument comprising modular units effectuating measurement anddetection of trace elements along with minor and major elementalcomposition of any liquid and/or solid samples. Another embodiment is asingle LIBS instrument capable of measuring every element of thePeriodic chart that has a known optical spectrum simultaneously.

The present disclosure provides a novel apparatus for performing rapidchemical analysis of liquid samples using laser induced breakdownspectroscopy (LIBS). The apparatus includes a pulsed laser, a pump tointroduce liquid sample material, a nebulizer to generate an aerosolizedportion of the liquid, means to confine and/or control a flow pattern ofthe gaseous aerosol, and means to exhaust and/or collect the aerosol.The apparatus also comprises an optical system that can steer and/orfocus a laser beam to a predetermined location in the aerosol flow toproduce an emissive plasma plume comprising the aerosolized samplematerial. There is also an optical system that can gather a portion ofthe characteristic light emitted from the plume and couple said lightinto one of more spectrometers having respective detectors. Apredetermined combination of a spectrometer comprising a wavelengthseparating element and a detector are configured to measure spectraldata and generate intensity values, wavelength values and compositionvalues of one or more elements of the sample optimally. The spectrometercan have a scanning single channel configuration, a cross-dispersionechelle configuration, or a multi-channel configuration of severalspectrometers. The detector can be a high speed triggered/gated detector(e.g. charge coupled device “CCD” or complementary metal oxide silicon“CMOS” camera), a high-speed intensified detector (e.g. intensifiedcharge coupled device “ICCD”), an electron multiplying charge coupleddevice (EMCCD), or an array of photodiodes or photomultipliers. Apredetermined instrument configuration suitable for analysis of bothliquid and solid samples can have a single wavelength separation elementand detector array (a spectrometer) or use respectively separate and/ordifferent spectrometers for liquid and solid analyses, depending on theapplication.

Another aspect of the present disclosure includes a novel method ofmeasuring major, minor and trace elements in liquid samples using theLIBS apparatus. The method includes generating a narrow stream ofaerosol from a portion of a liquid sample which is carried by a flow ofa carrier gas such as air, nitrogen and/or any inert gas selected basedon the characteristics of the sample and the types of elements beingdetected. A laser beam with a preselected power, frequency, andduration, and wavelength values is directed to and focused on apreselected region of the aerosol stream, which generates a luminousplasma plume comprising an atomized, partially ionized, and opticallyexcited molecular species of the sample material. The emission spectrafrom the aerosolized sample material is recorded by a device preferablyan optical spectrometer including an ICCD, EMCCD, CMOS or CCDdetector(s) which digitizes the spectral data for further computationalanalysis in real time. The optical spectrum provides a signature of thechemical species present in the sample. Then the concentrations of oneor more specific chemical species in the sample are quantified usingpreviously known standard reference spectra.

Extremely viscous liquids and/or fluids that cannot be aerosolized canbe analyzed within a time scale during which they are substantiallyequivalent to solid samples. It has been found that sufficiently highviscosity materials do not splash during laser ablation. These materialscan be analyzed is the same manner as “solids”. In practice, dependingon the viscosity, it may be convenient or necessary to put the highlyviscous material in a small containers such as a beaker, or othercontainer that can in turn be on the solid sample stage within the LIBSapparatus. Venezuelan crude oil such as the NIST research materialRM-8505 is an example of a viscous material that can be measured as ifit were a solid sample, thus requiring no sample preparation (e.g.dissolving and/or diluting of viscous sample materials). It was observedthat laser ablation events produce voids (e.g. “craters”) on the surfaceof Venezuelan crude oil in a container. Such craters persist longer than30 seconds before the surface of the viscous crude is restored bygravity and surface tension.

The present disclosure also includes various embodiments for performingrapid chemical imaging of any solid samples in 2D and 3D using the LIBSdescribed herein. The embodiments provide a 2D and/or 3D elementalcomposition of a solid sample by mapping and effectuating LIBS analysisof a series of preselected sample sites in x, y and z axes, quantifyingand compiling these chemical composition data. The solid samples areplaced in a chamber operable to move in x, y and z axes independentlyusing translation motors. The sample chamber is built with a transparentwindow through which a collimated laser beam passes to ablate apreselected specific site of the sample. A compact CMOS camera providesmagnified images of the sample surface for visual inspection, monitoringand controlling the movement of the sample. Furthermore a triangulationsensor detects and measures exact position of the sample surface. Usingthe signal from the triangulation sensor, an ablating laser beam can befocused on a preselected sample site on the sample surfaceautomatically. The sample surface can be flat and/or curved. The samplechamber has an inlet and outlet openings allowing the flow of anunreactive carrier gas such as Nitrogen (N₂), Argon (Ar), Helium (He),and/or air through. The preselected gas carrier gas flow rate iscontrolled preferably by a mass flow controller. The apparatus includesa system computer with operation software that controls all workingfunctions of the instrument and through which a preselected protocoldepending on the application can be entered and executed to generate a3D chemical imaging of a solid sample.

The present disclosure also compromises a novel method for detecting andmeasuring major, minor and trace elements in solid samples with highspatial resolution in 2D and/or 3D using the LIBS described herein. Themethod includes a protocol of generating on a sample site at least onelaser ablation or a series of ablations in a predetermined pattern, forexample a grid of sample sites on the surface of a solid sample and at aspecific depth of a sample sensed by a triangulation sensor. Thespectral data of the individual laser ablation events can be used toform a chemical image of the sample and/or the spectra from any numberof laser ablations can be summed up together for averaging depending onthe structure and the material of the sample. Lateral resolution of theresulting chemical image is determined by a preselected ablation spotsize and a pattern used. Depth resolution is determined by preselectedenergy of laser pulses and a sample material. In some embodiments, therecan be more than 10000 sample ablation events to construct such as achemical image of a solid sample.

Further aspects of the present disclosure include novel methods formeasuring elemental composition of samples which are significantlysmaller than a laser spot size on the sample site, particularly analysisof samples with sub-micron (<1 mm) sizes and sub-nanogram (<1 ng)masses. Examples of such samples can include individual solid particleson a substrate such as filter paper, swipes, adhesive tape, or othersurfaces. The sample can be prepared by embedding of the minute samplein ice and/or other types of matrix materials to detect specificindividual particles using high spatial resolution LIBS. Additionally,biological tissue samples can be prepared by administration ofnanoparticles-based biomarkers and the distribution and interaction ofthe biomarker in the tissue can be analyzed using LIBS precisely. Thedisclosed method includes means of navigating through an embedded samplesurface images to place an inspected particle into a laser spot, andobliterating the whole particle located in a laser spot with a singlelaser pulse to obtain a spectrum corresponding to the select particle.Sensitivity of this method meets that of ICP-MS, which can measure onlyaverage elemental concentrations of all particles from an acid-digestedmacroscopic sample.

Further embodiments included in the present disclosure are thecapabilities of LIBS fully automated mode of all operations and the realtime computational analysis of digital spectral data to identify atleast partially chemical composition and characterize the elementalcomposition of a plurality of sample forms. The computational methodsenabling real time analysis of elemental composition include quantifyingthe elements according to the known spectral standards, and performingexplorative (visualization), qualitative (classification), orquantitative (calibration) statistical analysis. One protocol toquantify emission spectra data includes univariate calibration usingstandard reference materials and/or the calibration standards directlyadded to the aliquots of analyzed sample (standard additions) dependingon the applications. The spectral analysis protocol is performed usingstatistical analysis methods often referred to as “chemometric analysis”or “chemometrics”. The chemometric algorithms are operable to compare areal-time measured spectrum to the spectra stored in a referencedatabase in memory of a system computer. This method allows users todetect, identify, and quantify chemical elements present in a sampleusing an automated mode of operation. Accordingly, simplified operationshowing symbolic red, amber or green “lights” can be realized for rapidmonitoring or quality control of the samples. Alternatively, allgenerated and calibrated spectral data, and/or elemental concentrationscan be presented on a graphical user interface.

Some embodiments include a true universal LIBS analyzer that can measurethe elemental composition, major, minor and trace elements in any solidor liquid sample. The disclosed apparatus requires only about 750 μl ofa liquid sample, or only a few nanogram of solid sample, consumes onlylow power (<400 W) and generates no acidic waste. The capability of LIBSto measure major elements within most materials, particularly of organicmaterials comprising Carbon (C), Hydrogen (H), Oxygen (O), and/orNitrogen (N) facilitates normalization and correction of signals fromthe trace elements on the distribution of major matrix elements toimprove accuracy and precision of quantitative analysis. This isespecially important for heterogeneous matrices and matrices of variabledensity, such as biological matrices.

Other features will become apparent from consideration of the followingdescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Various embodiments are illustrated in an exemplary manner by theaccompanying drawings. The drawings and accompanying description shouldbe understood to explain principles of the embodiments rather than belimiting. Other embodiments will become apparent from the descriptionand the drawings:

FIG. 1 is a simplified diagram of a laser ablation apparatus embodiment.

FIG. 1A is another diagram of a laser ablation apparatus embodiment.

FIG. 2 illustrates a detail of a laser ablation graphical userinterface.

FIG. 3 illustrates a plan view of a testing protocol.

FIGS. 4A and 4B illustrate side views of a topology of a sampleaccording to an embodiment.

FIG. 5 illustrates a plot of spectral information according to anembodiment.

FIG. 6 illustrates a plot of intensities of known standards according toan embodiment.

FIG. 7 illustrates a process flow diagram for a method of ablating.

FIG. 8 is a simplified diagram of apparatus for laser induced ablationspectral analysis including LIBS and LA-ICP-MS.

FIG. 9 is a simplified diagram of apparatus for laser induced ablationspectroscopic analysis comprising collection optics modules and fiberbundles to couple optical emission to spectrometers.

FIG. 10 is a simplified diagram showing an apparatus for LIBS havingoptical collection modules and lightguides for internal and optionalspectrometer modules.

FIG. 11 is a simplified diagram of apparatus for laser induced ablationspectroscopic analysis for LIBS having one optical collection modulecoupled to an optical fiber bundle having split ends for an internalspectrometer and an optional spectrometer module.

FIG. 12A is an isometric view of an optical frame for a LIBS apparatus.

FIG. 12B is an overhead view of the optical frame shown in FIG. 12A.

FIG. 13 is a side view of the optical frame shown in FIGS. 12A and 12B.

FIG. 14A illustrates a schematic diagram of an embodiment for analysisof a liquid or a solid sample.

FIG. 14B is a simplified diagram showing optical elements in anembodiment for redirecting a laser beam from a liquid analysisconfiguration to a solid sample analysis configuration as depictedgenerally in FIG. 14A.

FIG. 15 shows lower limits of detection for elements in aqueous ornonaqueous solutions in an ICP-OES analysis and using an embodiment ofthe disclosed LIBS apparatus.

FIG. 16 shows spectra of high viscosity NIST reference materials RM-8505and SRM-1634c in an embodiment.

FIG. 17 shows LIBS spectra of Mg peak at 279.5 nm from a gasoline sampleand various concentrations of Mg calibration standards in PremiSolVsolvent.

FIG. 18 shows a multivariate calibration graph using LIBS to determinethe C/H ratio in organic solvents after an embodiment.

FIG. 19 shows an example principal component analysis of LIBS spectra.

FIG. 20 presents the LIBS and ICP-OES measurements of Mg inlow-viscosity nutrient liquid samples in an embodiment.

FIG. 21A illustrates sample sites in profiling various layers of a3-dimensional solid battery cell structure.

FIG. 21B shows the spectral intensities from various layers in FIG. 21A.

FIG. 22A is an image of a mineral sample and a mapped area according toan embodiment.

FIG. 22B shows a distribution of fluorene in the mapped area of FIG.22A.

FIG. 22C shows a distribution of oxygen in the mapped area of FIG. 22A.

DETAILED DESCRIPTION

Systems, methods, compositions, and apparatus for providing novel laserinduced ablation spectroscopy are disclosed. In various embodiments, anapparatus comprises a sample site position sensor, stage position motorsoperable to move the stage in three independent spatial coordinatedirections, and a stage position control circuit to move an analysissample site to selected coordinate positions for laser ablation, with nohuman interaction. The ablation of material from an analysis sample sitecan displace its position from a point where the laser beam has apredetermined spot size. The embodiments can have a laser positionsensor to detect a change in the position of the sample site andgenerate a displacement signal operable for the stage position controlcircuit to return the sample site to an original position using thestage motors.

In various embodiments, collection optics can be useful to gather lightfrom a plasma plume produced with a laser ablation. The collectionoptics can couple the gathered light into a light receiving end of alightguide through which the light can be transmitted to a spectrometer.The lightguide can be a single fiber optic bundle including a pluralityof optical fibers held generally parallel to one another in a geometricarrangement. However, in some embodiments, the various fibers in thesingle bundle (trunk section) at the (light receiving) end can beadvantageously subdivided into smaller bundles (e.g. a plurality ofbranches) to convey various portions of the light to a plurality ofspectrometers. Depending on the application, different branches canconvey distinct preselected fractions of the light from the trunk todifferent spectrometers. For example, in an embodiment one branch fromthe trunk fiber bundle can convey a first portion of the light to abroadband spectrometer operable to analyze a relatively wide spectralsegment, and a different branch can convey a second portion of the lightto a high dispersion spectrometer operable to measure minorconcentrations and/or trace elements. Emissions from a plasma plume canthereby be simultaneously analyzed in various ways using spectrometershaving distinct and/or complementary capabilities. For example, aspectrometer having a high speed gated detector, a spectrometer having ahigh speed intensified detector (i.e. an ICCD), a spectrometer having anelectron multiplying charge coupled device (EMCCD), and/or aspectrometer having enhanced sensitivity and/or selectivity inparticular wavelength regions and or at particular wavelengths, can allreceive and analyze radiation from the same plasma plume carried throughdifferent branches. It will be understood that various advantageousspectrometer characteristics may not be exclusive. For example, aspectrometer can be configured with a type of detector particularly wellsuited to the characteristic light throughput (efficiency) andresolution of its dispersive element(s), as well as being selectivelygateable to detect light exclusively in a preselected interval followingeach laser pulse. In particular, an intensified charge coupled devicedetector can be intensified to provide very high sensitivity relativesensitivity, and/or can be synchronously gated on during a shortinterval following each laser pulse to discriminate against backgroundcontinuum radiation.

The terminology herein is for the purpose of describing particularembodiments and is not intended to be limiting of the invention. It willbe understood that, although the terms first, second, etc. may be usedto describe various elements, these terms are only used to distinguishone element from another, and the elements should not be limited bythese terms. For example, a first element could be termed a secondelement, and similarly a second element could be termed a first element,without departing from the scope of the instant description. As usedherein, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” “including,” and/or “having,” as used herein,are open-ended terms of art that signify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. Reference in the specification to “one embodiment”, “anembodiment”, or some embodiment, etc. means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment. The appearances of the phrase“in one embodiment” in various places in the specification are notnecessarily all referring to the same embodiment, nor are separate oralternative embodiments mutually exclusive of other embodiments.

As used here, various terms denoting spatial position such as above,below, upper, lower, leftmost, rightmost and the like are to beunderstood in a relative sense. The various aspects of the apparatusesdescribed herein are operable without regard to the spatial orientationof the apparatuses as a whole. For example, an apparatus can beconfigured in a vertical orientation or in a horizontal orientation.Hence a component or module that is described as being above anothercomponent or module in a first embodiment having a first orientation,could equivalently be described as being to the left of the othercomponent or module in an equivalent second embodiment configured to bein a second orientation 90 degrees counterclockwise with respect to thefirst.

The term module refers to a distinct unit that is operable to perform anidentifiable function. A module can be a self-contained physical unit orpiece of equipment. A module can also be a logical component effectuatedby a processor and tangible media having instructions and/or data thatare operable for the processor to perform the identifiable function. Theterm automatic refers to a module, service, or control system that isoperable to perform with no human interaction. Monitoring or sensingrefers to measuring a physical quantity. Monitoring is often performedfor the purpose of regulation or control.

The term gas or gas phase species as used herein includes species notbound to each other that have thermal and/or directed motion in a gasphase. The term is not limited by a specific value of a mean free pathbetween collisions. Hence the term “gas phase species” includes variousdifferent species in vapors, atomic or molecular beams, and gaseoussuspensions such as aerosols, and the like.

A lightguide refers to a transmission channel for the directedtransmission of luminous electromagnetic radiation over a distance. Alightguide can include one or more fine filamentary optical fiberscomprised of dielectric material such as silicon dioxide, a transparentpolymer, and the like. The outer surface of each individual opticalfiber can have a cladding of relatively lower refractive index. Alightguide have a cross section that is circular, rectangular, U-shaped,ribbon-shaped, and others. The cross section can be solid or it can behollow. By way of further example, a lightguide can be covered with ajacket comprised of transparent material, opaque material, and others.

The term spectrometer is generally used to identify an instrument thatcan used to view and/or analyze a characteristic of a substance. Withreference to LIBS, an optical spectrometer (also referenced as“spectrometer” and/or “spectrograph”) is an instrument operable toseparate and detect different wavelength components in electromagneticradiation within a range of about 180 nm to 1000 nm (ultraviolet toinfrared). However, depending on the context, the term opticalspectrometer (“spectrometer”) can also be understood to mean thesubsystem in an optical spectrometer operable to disperse and/orseparate various wavelength components of the electromagnetic radiation(e.g. the term spectrometer being understood to mean a monochromator orpolychromator apart from any detector). The intended meaning can beunderstood from the context.

The term “detector”, as used here, means a plurality of elementalelectromagnetic radiation sensors in an array. The array can be a lineararray or a two dimensional array of electromagnetic radiation sensors.Linear and two dimensional arrays of CMOS (complementary metal oxidesemiconductor) photosensors, CCD (charge coupled device) photosensors,ICCD (intensified charge coupled device) photosensors, EMCCD (electronmultiplying CCD) photosensors, and one and two dimensional arrangementsof multiple photodiodes, photomultipliers, and others can be usefuldetector arrays (“detectors”) for LIBS, depending on the embodiment. Theterms photosensor and photodetector, as used here, are synonymous.

The term a mass spectrometer (MS), as used herein, references aninstrument that can separate and detect ions gas based on their chargeto mass ratio. The term inductively coupled plasma mass spectrometer(ICP-MS) will be understood to mean an analysis instrument based onionizing gaseous species in a high temperature inductively coupled(thermal) plasma, extracting such ionized species from the plasma, anddetermining their composition with a mass spectrometer.

The present teachings may be embodied in various different forms. In thefollowing description, for purposes of explanation, numerous specificdetails are set forth in the description and drawings in order toprovide a thorough understanding of the various principles. Furthermore,in various instances, structures and devices are described and/or drawnin simplified and/or block diagram form in order to avoid obscuring theconcepts. However, it will be apparent to one skilled in the art thatthe principles can be practiced in various different forms without thesespecific details. Hence aspects of the invention should not be construedas being limited to the embodiments set forth herein.

FIG. 1 shows a schematic overview of a laser ablation apparatus 100according to the present invention. The apparatus 100 generally includesa pulse laser 102, a stage 106, a position sensor 112, a spectrometer120 and a system computer 140. The apparatus 100 is configured togenerate laser pulses from the pulse laser 102. The laser pulses arefocused onto a sample 105 with a lens 104 to produce a plasma plume 114of the sample 105 at a sample site 110. The position sensor 112 iselectrically coupled with the system computer 140 for sending adisplacement error signal to automatically correct positioning of thestage 106 during an ablating process as describe further below. Theapparatus 100 can include a system frame for housing the variouscomponents described herein. The system frame can include an air filterfor filtering contaminants produced during the ablating process.

The pulse laser 102 in an exemplary embodiment comprises a neodymiumdoped yttrium aluminum garnet (Nd:YAG) laser for generating energy inthe near infrared region of the electromagnetic spectrum with awavelength of 1064 nm. The pulse duration can be approximately 4 ns forgenerating a laser beam with a power density that can exceed oneGW/cm·sup.2 at a focal point or ablation impact point. The laser 102 canhave a repetition rate of approximately 10 hz or alternately lower than10 hz in some embodiments. Alternatively, the pulse duration can vary totens or hundreds of nanoseconds. In another embodiment, the pulseduration can be shortened to ultra short femtoseconds. The lens 104comprises an objective lens used to focus the laser beam on a surface ofthe sample site 110. The laser beam can be focused to a spot size ofapproximately 10-500 micrometers on the sample site 110. In an exemplaryembodiment, the laser beam can be focused to a spot size ofapproximately 150-200 micrometers on the sample site 110.

In an alternative embodiment, a spark generator can be used as theablation source instead of the pulse laser 102 or a spark can besynchronized and used in combination with the laser pulse. An electricspark is passed through a sample material until the sample materialreaches a temperature where characteristic spectral emissions can bedetected. In an exemplary embodiment, the electric spark can becontrolled in an argon atmosphere. A person of ordinary skill in the artcan appreciate the construction of such spark generators in sparkspectroscopy systems.

A dichroic mirror 107 is used for directing the laser beam toward thesample site 110 and a mirror 109 allows viewing of the sample site 110using a video camera 116.

The stage 106 includes an attached array of ‘x-y-z’ motors 108 forproviding translation of the stage 106 in a three dimensional space. Thex-y-z motors can comprise suitable stepper motors driven by steppingmotor controllers (not shown), as known by a person of skill in the art.In one embodiment, the stage 106 can have a translation rate ofapproximately 10 cm/s. The stage 106 can include a sample securingmeans.

The position sensor 112 preferably comprises a laser triangulationsensor. The position sensor 112 preferably uses the principle oftriangulation to determine changes in height of the stage 106 and theassociated sample 105. As shown in greater detail in FIG. 1A,triangulation occurs when the position sensor 112 emits a triangulationlaser beam 113 that is focused on the sample site and a first reflection115 a is sensed by a photodetector within the position sensor 112. Achange in height of the sample site 110 causes a displacement in thetriangulation laser beam 113 to produce a second reflection 115 b and adisplacement signal generated by the position sensor 112 is communicatedto a system computer 140. The system computer 140 provides positioninginformation to maintain an optimum height of the sample site. Theposition sensor 112 can comprise a suitable laser displacement measuringdevice as known to a person of skill in the art. In one embodiment, thetriangulation laser 113 coincides with a spot circle of the laser 102generated at the sample site. The triangulation laser 113 can also beused as a targeting marker when selecting a specific point on the samplesite 110 as seen with the video camera 116 as the triangulation laser113 can produce a visible spot on the surface of the sample site 110.

The spectrometer 120 (FIG. 1 ) collects electromagnetic information fromthe plasma plume 114. The spectrometer 120 can be a monochromator or apolychromator with a detector. The electromagnetic information includesspectral information identifying an elemental composition of the samplesite 110. A spectral range for the spectrometer 120 can be chosen tosuit different applications. In an exemplary embodiment the spectralrange can be approximately 35 nm for observing a portion of theelectromagnetic wavelength range. Alternatively, the spectrometer 120can detect electromagnetic radiation in a range of 200 to 900 nm.Collection optics 122 receive light and plasma lumina generated from theplasma plume 114 and transmits the light and plasma lumina through afiber cable 124 to the spectrometer 120. The collection optics 122 canbe orientated horizontally as shown in FIG. 1 . Alternatively, thecollection optics 122 can be orientated at any angle above the sample105 surface plane. A mirror (not shown) within the spectrometer 120reflects the plasma lumina to a grating that disperses the plasmalumina.

An intensified charge coupled device (ICCD) or detector 130 is coupledwith the spectrometer 120 for detecting the dispersed plasma lumina. Thedetector 130 provides the detected plasma lumina to the system computer142. The system computer 140 generates spectral information from theplasma lumina of the laser plume 114. The spectral information includesintensity data representing elemental information and composition of thesample site 110. The spectral information can be produced on a display142.

The detector 130 provides increased resolution and greater selectivityof the spectral information. The detector 130 includes a microchannelimage intensifier plate. The intensifier plate is preferably gatedduring period of time when the plasma plume 114 emits characteristicatomic emission lines of the elements. This period coincides with anoptimum plume luminance period. This period follows emission ofcontinuum radiation. Continuum radiation lacks useful specific speciesor elemental information. In one embodiment, a delay generator (notshown) can be included to provided gating of the detector 130 to allowtemporal resolution of the detector 130 response time. Alternativeembodiments of the detector 130 can include a detector other than anICCD, for example a suitable charge coupled device (CCD) or suitablephotomultiplier. Accuracy of the spectrometer 120 and detector 130 inone embodiment can generate compositional data in the range of 20 ppm orless. Alternatively, the accuracy can be in the range of a few %. Inanother embodiment, the accuracy can be in the range of 1%, which isapproximately 10,000 ppm.

The system computer 140 can include application software and acontroller in the system computer 140 for providing synchronization ofthe laser 102, spectrometer 120, detector 130, position sensor 112 andthe x-y-z motors 108 positioning of the stage 106. The system computer140 is electrically coupled with the laser 102, spectrometer 120,detector 130, position sensor 112, the x-y-z motors 108 and the camera116. The system computer 140 includes a display 142 for displayingspectral information. The system computer 140 can present the spectraldata generated on the display 142. Alternatively, a separate personalcomputer can also be coupled with the system computer 140 for separatelyanalyzing the spectral information. The system computer 140 can includea power controller to regulate power to all the apparatus 100components.

The application software decodes the spectral information from thedetector 130 and facilitates analysis of the spectral information andgenerates composition information of the sample 105. In one embodiment,the intensity data of an elemental peak is subtracted from backgrounddata of the elemental peak to calculate a change in intensity (delta I).The application software allows setting of certain parameters forperforming the laser ablations of the sample site 110. A laser spotcircle size can be set as a parameter and can be consistently andprecisely maintained through the laser ablation process described infurther detail below. Alternatively, a z value for the sample site 110can be set as a parameter and can be consistently and preciselymaintained through the laser ablation process. The spot circle increasesor decreases depending on the change in height of the sample site 110.Keeping the laser 102 spot circle precisely adjusted insures that thesample site 110 produces the plasma plume 114 with consistent optimumplume luminance. Height changes in the sample site can be detected bythe position sensor 112 and a correction to the height of the samplesite 110 is generated by the controller within the system computer 140.The application software and the controller generate correction signalsto reposition the height of the stage 105 after each laser ablation ofthe sample site.

FIG. 2 shows a representative graphical user interface (GUI) 200according to an embodiment of the present invention. The GUI 200includes a first data window 218 and a second data window 220. The firstdata window 218 provides real-time video of a sample site 110. A spotcircle 118 can be observed on the sample site 110 during and followingan ablation. The second data window 220 provides spectral informationgenerated from the system computer 140. In an exemplary embodiment, thespectral information includes a waveform 222 representing intensity andwavelength data of a sample site ablation.

FIG. 3 shows a top view 300 of a protocol for ablating a sample 305according to an embodiment of the present invention. The protocolincludes ablating multiple sample sites 312. In an exemplary embodiment,the sample sites can be uniformly and evenly distributed throughout asurface of the sample 305. Alternatively, the sample sites 312 can berandomly distributed through the surface of the sample site. The numberof sample sites 312 ablated can vary depending on a particular sample ora particular application. The spectral data of the individual laserablation sites can be used to form a chemical map of the sample surfaceor the total number of laser ablations for the sites can be averagedtogether. In one embodiment, the number of sample sites comprisestwenty. Alternatively, the number of sample sites can be ten or fewer.In another embodiment, the number of sample sites can be thirty or more.

The protocol 300 can include a specific number of pulse laser ablationsper sample site 312. Heterogeneous material can include elements havingvarying thermal properties. A single shot laser ablation can vaporizedisproportionately more volatile elements than the less volatileelements. Spectral information from a single ablation may not be areliable indication of the composition of the sample 305. In anexemplary embodiment, the number of laser ablations per site comprisesthree laser ablations. Alternatively, the number of laser ablations persite comprises two. In another embodiment, the number of laser ablationsper site comprises a single laser ablation. In still another embodiment,the number of laser ablations per site comprises four or more laserablations.

FIGS. 4A and 4B show side views of a first sample 405A and a secondsample 405B according to an embodiment of the present invention. Thefirst sample 405A comprises a material having sample sites 410A withsubstantially uniform topology. The height of the sample sites 410A aresubstantially the same. The second sample 405B, however, comprises amaterial having sample sites 410B with erratic or varying topology. Theheight of the sample sites 410B can be different. The apparatus 100 isconfigured to provide consistent spectral data for either the uniformsample sites 410A or sample sites 410B with varying heights. The systemcomputer 140 adjusts the height of the stage 106 to achieve the optimalplasma lumina.

FIG. 5 shows a plot 500 of spectral data according to an embodiment ofthe present invention. The plot 500 includes a waveform plotted along awavelength (nm) versus an intensity (a.u.). An elemental peak ‘A’ canrepresent the spectral information for the element Lead (Pb). Theelemental peak ‘B’ can represent spectral information of a differentelement.

FIG. 6 shows a plot 600 of compositional data 600 according to anembodiment of the present invention. The plot 600 includes a waveformplotted along a composition (nm) versus an intensity (a.u.). The plot600 is generated by performing laser ablation according to the methoddescribed herein on a known standard sample. The known standard producesintensities I1, I2 and I3 for associated elements at the respectivecompositions 34 ppm, 146 ppm and 406 ppm. Quantitative analysis ofdifferent elements of a particular sample is performed by comparingspectral data of the particular sample with the compositional data 600.For example, spectral information obtained from analysis with theapparatus 100 can include intensity 14. The quantity of the element canbe approximated to 90 ppm.

FIG. 7 shows a process flow diagram for a method 700 of laserspectroscopy according to an embodiment of the present invention. Thelaser ablation apparatus 100 (FIG. 1 ) is used as an example. The method700 begins at the step 710. In one embodiment, the method 700 can befully automated using application software included in the systemcomputer 140. A specific protocol can be entered into the applicationsoftware instructing the application software of desired parameters orsettings for the apparatus 100. Alternatively, the method 700 can bemanually performed. At the step 720, a laser pulse is generated toablate the sample site 110 into an emissive plasma plume. A real-timevideo image of the sample site 110 is generated on a first window 218 ofthe GUI 200. The real-time video is received from the video camera 116.The plasma plume 114 is analyzed by the spectrometer 120 and thedetector 130. The plasma lumina and the electromagnetic radiationgenerated by the plasma plume is optically communicated to thespectrometer 120 and detected by the detector 130. The position sensor112 provides a displacement signal to the system computer 140 indicatingany change in the height of the sample site 110. The system computerreceives spectral information from the spectrometer 120 and the detector130.

At the step 730, the system computer 140 generates spectral andwavelength information for presentation on the display 142. In oneembodiment, intensity and wavelength data are represented as waveformson the GUI 200. The waveform is presented in a second window 220 of theGUI 200 and includes the intensity and wavelength data. In anotherembodiment, a second waveform is superimposed on the first waveform 222in the second window 220. The second waveform can include additionalspectral information. For example, particle imaging information,tracking information or scaled or gated representations of the firstwaveform 222.

At the step 740, the steps 720 and 730 are repeated for each sample siteon the sample. The spectral data for a total number of laser ablationsfor the sample site 110 can be averaged together. In an exemplaryembodiment, the total number of laser ablations for the sample site 110equals three laser ablations. The spectral data of the three laserablations are averaged together to generate a ‘site sum’. The site sumis a reliable and accurate representation of the elemental compositionof the sample 105 at the sample site 110. Alternatively, the site sumcomprises spectral data from two laser ablations. In another embodiment,the site sum comprises spectral data from one laser ablation. In stillanother embodiment, the site sum comprises spectral data from four ormore laser ablations.

At the step 750, the site sum can be compared with spectral informationgenerated from performing the method described herein on a knownstandard material. The known standard material comprises specific knownelements at a known composition. Laser spectroscopy performed on theknown elements generates known spectral data including known intensityvalues. An elemental composition for the sample site 110 can beapproximated by comparing the site sum with the known standard spectraldata.

At the step 760, the steps 720 through 750 can be repeated for one ormore additional sample sites to generate additional site sums. Thespectral data for the total number of site sums can then be averagedtogether. In an exemplary embodiment, the total number of site sumsequals twenty. The spectral data of the twenty site sums can be averagedtogether to generate a ‘sample sum’. The sample sum is a reliable andaccurate representation of the elemental composition of the sample 105as a whole. Alternatively, the total number of sites sums can be ten orfewer. In another embodiment, the number of sites sums can be thirty ormore.

The apparatus 100 can perform laser ablation or laser induced breakdownspectroscopy (LIBS) on a variety of materials. The materials can beheterogeneous or homogeneous solids or semi-solids. Alternatively, thematerials can comprise a liquid or even a gas. In another embodiment,the apparatus 100 can be used for LIBS on biological materials. Analysisof biological material can include building a library of known spectralsignatures including elemental and compositional data for specificbiological material. The spectrometer 120 can collect and detect withthe detector 130 spectral information on a broad range from 200 to 900nm. An unknown biological sample can be compared with the library todetermine the biological substance. The method ends at the step 780.

In an alternative embodiment, the method 700 can be used in a remoteconfiguration. The sample material is positioned in a location that isremote from the ablation source or laser. A telescopic device can beintegrated with the apparatus 100 to provide optical coupling of plasmalumina. The generation and analysis of spectral data can proceedsimilarly as described herein. Furthermore, other spectroscopies, inplace of and/or in addition to optical emission spectroscopies can beused to obtain characteristic ablation spectral data within the scope ofthe present invention. For example, laser ablation inductively coupledplasma mass spectrometry (LA-ICP-MS) can be applied in conjunction withand/or as an alternative to the LIBS technique described herein.

Still further embodiments can be understood with respect to FIGS. 8-13B.Like numerals in FIGS. 8-13 . Like numerals in FIGS. 8-13 designatecorresponding elements.

FIG. 8 is a simplified drawing of a system for laser induced ablationspectral analysis of a sample. The system has a movable stage 8225coupled to x-y-x translation motors (not shown) that can move a sample8310 on the stage in three independent directions. The system also has alaser 8205 that can emit a pulsed laser beam 8210, and has variousoptical elements such as a mirror 8220, laser beam focusing opticsmodule 8416 and/or others that can cooperatively focus the laser beamonto a selected sample site 8217 for ablation. The sample 8310 and stagecan be in an unreactive gaseous atmosphere confined within enclosure8200. The atmosphere in the enclosure can be transparent at wavelengthscomprising pulsed laser beam and/or characteristic spectral emissionemanating from the plasma plume 8010. In a preferred embodiment, thepulsed laser 8205 can be a Nd YAG laser emitting a pulsed laser beamwith a near infrared wavelength of 1064 nm, and the unreactiveatmosphere can be inert gas such as helium and/or argon.

However, an ultraviolet wavelength selected from among 193 nm, 266 nmand 193 nm is preferred for the ablation for some applications,particularly when performing analyses using ICP-MS. UV wavelengths canprovide a better sample of gaseous species from a sample site bycomparison to a more conventional pulsed laser wavelength in the nearinfrared. Short UV wavelengths can be generated as harmonics of longerwavelength excimer and/or solid-state lasers as will be understood bythose having ordinary skill in the art.

Characteristic spectral emission emanating from the plasma plume 8010generated by ablation can be gathered with a collection optics module8410. The collection optics module can couple the spectral emission intoa lightguide 8230. The lightguide can transmit the optical emission toan optical spectrometer comprising wavelength separation unit 8510 anddetector 8550. The collection optics module can include lenses 8412,8414 and/or other optical elements and is disposed in a preselectedposition and orientation by optical frame 8440. Further details of anoptical frame structure 8440 are disclosed in FIGS. 12A, 12B and 13 . Asshown in FIG. 12A, the laser beam focusing optics module 8445 is securedto frame 8440 in a position where it can center a precise laser spotcircle 9510 of predetermined size in plane 9460 on a point 9500. Plane9460 is a preselected distance 9450 below optical frame 8440.Accordingly, stage 8225 can movably translate a selected sample site8217 (also see FIGS. 9-10 ) to the center laser spot circle position toperform precise and consistent laser ablation of material from theselected site.

As can be understood with respect to FIGS. 10-13 , the optical frame8440 has support substructures 8415, 9415 operable to secure collectionoptics modules 8410 and/or 9410 in a preselected position withrespective central axis/axes 8416 and/or 9416 of each collection opticsmodule aimed at a situs 9300 of the plasma plume. This arrangementpositions each laser ablation and its ensuing plasma plume in the samelocation relative to the optics support structure 8440. Accordingly,each optics support substructure 8415, 9415 can hold a respectivecollection optics module 8410, 9410 in a fixed position and orientationthat can optimize light collection from a plasma plume arising from thespot circle position.

In various embodiments, a gas flow system such as shown with respect toFIG. 8 can maintain an atmosphere of unreactive carrier gas insample/stage enclosure 8200. A source of pressurized unreactive gas 8350can be coupled to a flow controller 8355 through a fluid channelcomprised of conventional tubing, pipe and/or fittings. The flowcontroller 8355 can deliver a selected flow rate of the carrier gas toenclosure 8200 through fluid passage 8365. Flow controller 8355 can be apneumatic flow controller, an electronic mass flow controller, a fixedorifice, and others. The flow rate can be controlled using a computer8710 to actuate the flow controller and/or provide a setpoint by way ofa communication channel represented by the dashed line between acomputer 8710 and flow controller 8355.

In some embodiments, gaseous laser ablation products 8215 generated inchamber 8200 can be transported in the carrier gas from enclosure 8200to an inductively coupled plasma-mass spectrometer (ICP-MS) 8100 throughflow channel 8366. In various embodiments, the gaseous laser ablationproducts can include permanent gases, vapors, molecular clusters,suspended particles, aerosols and/or others. The inductively coupledplasma-mass spectrometer (ICP-MS) 8100 is operable to perform a furtherspectral analysis of the ablation products based on the mass of ionizedspecies. In various embodiments, the ICP-MS comprises an inductivelycoupled thermal plasma sustained in an inert carrier gas such as argon.Those having ordinary skill in the art will recognize that thermalplasma sustained in the ICP-MS 8100 have sufficiently high temperature(over 5000 K) to ionize the gaseous laser ablation products. Ionizedproducts from the thermal plasma are introduced into a mass analyzerwithin the ICP-MS where they can be separated and identified based oncharacteristic charge to mass ratio. Accordingly, the ICP-MS analysiscan provide additional information useful to augment, improve, and/orconfirm an emission spectroscopy determination of sample sitecomposition based on lumina from the plasma plume.

It has also been found that ICP-MS may not be particularly effective todetermine relative relatively light elements (atomic number less thanabout 10) and elements generally found in organic compounds (carbon,hydrogen, oxygen and nitrogen). In this regard, it has been found thatthe LIBS analysis can complement and quantify the concentrations ofvarious elements that may not be acceptably measured using ICP-MS alone.Furthermore, it is difficult to measure high concentrations of elements(bulk composition analysis) in an ICP-MS while simultaneously performingtrace level chemical analysis with the same instrument. On the otherhand, ICP-MS is highly sensitive and can perform trace leveldetection/analysis at levels as low as 1 part per billion, and undersome circumstances even lower levels are operable. It has been foundthat a combination of laser ablation emission spectroscopy and laserablation ICP-MS can determine both high concentration level analysis aswell as trace levels at 1 ppm or even 1 ppb of a single sample site,which could not be performed using either laser ablation emissionspectroscopy or laser ablation ICP-MS alone. Yet another advantagehaving both techniques in combination arises from an ability to detectpulse-to-pulse variations in the amount of ablated material based on asignal level in from wideband emission spectra. The emission signals canbe useful to normalize and/or correct the ICP-MS mass/charge intensitiesthereby improving accuracy.

A system with respect to FIG. 8 can include at least one computer 8710.The computer comprises machine readable media operable to store data andinstructions and a processor that can read the data and perform theinstructions. Furthermore, media has various modules operable toeffectuate various control functions, control loops, displays, humaninterfaces, and others. The dashed lines 8720 shown in FIG. 8 representcommunications channels between the computer and various systemcomponents such as pulsed laser 8205, ICP-MS 8100, an opticalspectrometer wavelength separation unit 8510, a spectrometer detector8550, an electronic flow controller 8355, and a stage positioncontroller for x-y-z stage 8255. The system can also includecommunications channels for a sample site position sensor, and otherphysical and/or software components not shown in FIG. 8 . It will berecognized that a communication channel can be implemented in variousdifferent ways. For example, data and/or instructions can be carried byway of physical media as point to point wiring, over a parallel bus,over serial and/or parallel fiber optic connections, with a virtualcircuit in a network protocol layer, and/or others.

It will be understood that various embodiments with respect to FIG. 8can further include a number of additional elements and structuresdisclosed in relation to FIGS. 1-7 above. These elements are beenomitted from the drawing to avoid obscuring other concepts simplify theexplanation. By way of example, a system with respect to FIG. 8 caninclude a video camera, a sample site position sensor and an x-y-z stageposition controller in a stage position control circuit, a triangulationlaser, and others. Furthermore, some embodiments do not include all ofthe elements and subsystems shown. For example, there are embodimentswith an ICP-MS. In these embodiments unreactive carrier gas fromenclosure 8200 can be vented into an exhaust line (not shown).

Other embodiments of a system for material analysis using LIBS can beunderstood with respect to the simplified diagram in FIG. 9 . A systemwith respect to FIG. 9 comprises a master system module 9400, and canhave an optional extension spectrometer module 9600. The master systemmodule 9400 can include any of the elements and/or structures disclosedwith respect to FIG. 8 , including elements not shown in FIG. 9 (e.g.the carrier gas components 8350, 8355, and others are omitted forclarity). The optical frame 8440 of master unit 9400 is operable tosupport a second collection optics module 9410. The second collectionoptics module can gather spectral emission from a plasma plume 8010 andcouple the light into a second lightguide 9240. Lightguide branchsegment 9241 can deliver spectral emission to extension spectrometer9600. In some embodiments lightguide segment 9240 in the master moduleand segment 9241 in the extension spectrometer module can be portions ofone single continuous fiber. In further embodiments, segments 9240 and9240 can be physically different fibers optically joined through aninterface connection between the master module and the extensionspectrometer module.

An operable system with respect to FIG. 9 can comprise a master systemmodule without any extension spectrometer 9520 (master only). The masteronly configuration can perform laser ablation optical spectroscopy usingspectrometer 9510. Furthermore, a master only system can be fieldreconfigured to add an extension module. An extension model upgrade canadd the capability to acquire emission spectra from a plume from themaster system module spectrometer 9510 and extension spectrometer 9520simultaneously. Spectral data from similar and/or different types ofdetectors in spectrometers 9510 and 9520 can be communicated to computer8710 through communication channels 8720. A collection optics module9410 to acquire plasma plume light emission for the extensionspectrometer module 9600 can be included in master unit module 9400 whenit is shipped from the factory, or a second collection optics module9410 can added to an optical frame 8440 in the field. Variousembodiments with respect to FIG. 9 comprise an optical frame 8440 havingcollection optics module support substructures 8415, 9425, shown withrespect to IGS. 12A, 12B and 13, to hold respective collection opticsmodules 8410 and 9410 in a preselected positions and orientations asshown.

As shown with in FIG. 13 , the supporting substructures 8415 and 9415can have mirror symmetry with respect one another to be in predeterminedpositions directing the central axis 8416, 9416 of each collectionoptics modules to a point 9300 equidistant from each module, where thepulsed laser 8205 spot circle can generate a precise plasma plume. Thecentral axes 8416, 9416 intersect an x-y plane parallel to the stage atequal angles 8419, 9419, from which each module can view from a plume at9300 and capture equal portions of the light through equal solid anglecones 9350, 9360 subtended by the collection optics modules.

In various other embodiments, a master system module can include one ormore of the additional spectrometers and structures shown in anextension module with respect to 9-11 (e.g. a single master module LIBSsystem can comprise various spectrometers, lightguides (optical fibers),and others disclosed with respect to FIGS. 9-11 ), within one physicalunit (the instrument).

Some further LIBS system embodiments can be understood respect to FIG.10 . A branched fiber optic lightguide 8880 can have a trunk bundle ofoptical fibers 8890 configured to gather light from an emissive plasmaplume 8010 into the plasma plume light receiving trunk end 8580 oflightguide 8880. In various embodiments, a collection optics module 8410shown in FIG. 10 can be useful to improve light gathering efficiency.Light from the plasma plume 8010 is gathered into the trunk end of thebranched fiber optic lightguide cable and transmitted through all of theoptical fibers in the trunk of the branched fiber optic cablelightguide. The truck bundle of fibers is subdivided among a pluralityof fiber optic cable branches comprising exclusive subsets of the entirebundle of optical fibers in the trunk. The subset portions of opticalfiber bundles in branches 8237 and 8239 run to respective distalterminal ends 8537 and 8539 of the respective branches. Portions ofplasma plume light can be transmitted through the exclusive subsets offibers in branches 8237 and 8239 into spectrometers 9510 and 9520through rends 8537 and 8539 of the respective branches.

In some embodiments, all of the fibers in a branched fiber opticlightguide have the same diameter. Furthermore, each of the fiber opticbranches 8237, 8239 can have different numbers of fibers. Accordingly,in some embodiments, luminous flux gathered through the light receivingtrunk end of the branched fiber optic cable 8890 can be divided amongthe split distal terminal ends in proportion to the number of fibers ineach branch. In a number of embodiments relative to FIG. 10 , the totalspectral power from collection optics module 8410 entering the entirebundle of optical fibers in the trunk 8880 of the branched cable throughtrunk end 8580, can be split to deliver a relatively smaller portion ofthe total power emanating from the branch terminal end 8537 of onebranch 8237 comprising a relatively smaller number of fibers, and asecond branch 8239 comprising a relative larger number of fibers candeliver a relatively larger portion of the total power emanating fromits branch terminal end 8539. The smaller portion of power can bedelivered to a high sensitivity and/or low efficiency spectrometer 9510,and the larger portion of the power can be delivered to a lowsensitivity and/or low efficiency spectrometer 9520. It will beappreciated that splitting total power in this manner can providerelatively more illumination where more power is necessary and/ordesired, and relatively less illumination can be directed to aspectrometer where light intensity from the collection optics modulemight otherwise saturate its detector.

Relative to systems having two independent collection modules and twoindependent lightguides disclosed with respect to FIG. 9 , use of a spitend lightguide, and/or split end lightguide optical power distributionsystem distribution (FIG. 10 ) can save the costs associated of a secondcollection module 9410 and/or second collection module support structureelements on the optical frame 8440.

Still further embodiments are disclosed relative to FIG. 11 . A systemwith respect to FIG. 11 can provide a first collection optics module8410 configured to optimize the amount of luminous power received byspectrometer 9510 through a conventional unbranched fiber opticlightguide 9230. Those having ordinary skill in the art will appreciatean unbranched fiber optic lightguide 9230 will carry a relativelygreater amount of light from the plasma plume to a spectrometer 9510, bycomparison to a branched fiber optic lightguide 8890 capturing the sameamount of light into an equivalent trunk cross section (the entirebundle of fibers in a unbranched fiber optic lightguide can be viewed asa trunk, since entire bundle in the light-receiving end run to thespectrometer 9510, whereas the light gathered into the receiving end ofthe branched fiber optic lightguide 8890 is subdivided among a pluralityof branches and spectrometers). Accordingly, in embodiments where thespectrometer sensitivity is low and/or or limiting, such as where aCzerny Turner spectrometer is used to examine a relatively narrowspectral region, it is often advantageous to use an unbranched fiberoptic lightguide 9230 in order to provide a relatively maximal amount oflight to a low sensitivity spectrometer 9510. An ICCD detector can beused to further enhance the sensitivity of this configuration.

Various embodiments can additionally include a collection optics module9410 coupled to the proximal principal (trunk) end of an n-way splitterminal end fiber optic bundle (e.g. a branched fiber optic lightguidewhere the number of branches n is two or more). Each branch has anexclusive subset of the full bundle of fibers in the trunk 8880 of thebranched fiber optic lightguide can convey spectral emission to aseparate spectrometer. An embodiment with respect to FIG. 11 comprises afiber lightguide assembly having 4 branch bundles 8240, 8250, 8260, 8270configured to couple light to 4 respectively different spectrometers9520, 9530, 9540 9550. Various further embodiments can have N differentspectrometers coupled to a collection optics module with using an N-waysplit branched fiber optic lightguide. There are also embodiments havinga plurality of collections optics, where at least two of the modules arecoupled to first and second pluralities of different spectrometers (e.g.N and M) using N-way and M-way split end fiber optic lightguides. Inthis regard, all of the spectrometers in system embodiments disclosedherein can be operable to simultaneous receive the spectral emissionemanating from each plasma plume generated in a laser ablation of asample site.

An LIBS system with the capacity to analyze the spectral emission fromthe plasma plume at an ablation site in real time, using a plurality ofoptical spectrometers to receive spectral emission simultaneously,and/or in tandem, has many advantages that enable superior analyticalcapability relative to prior art systems. Wavelength separating elements(monochromators, polychromators, filters, and others) as well as thedetectors (i.e. CCD, ICCD, EMCCD, and silicon photodiode detectorarrays, and others) useful in an optical spectrometer have absolute andspectral sensitivity limitations that can make it impractical and/orimpossible to have sufficiently high spectral resolution, sensitivity,spectral bandwidth, and temporal resolution in a single opticalspectrometer instrument that is operable to broadly determine acomposition of unknown samples by LIBS multiwavelength analysis in realtime. However, an individual spectrometer can be optimized to enhancesensitivity, resolution, and/or temporal resolution over limited rangewavelengths. Accordingly, a plurality of optical spectrometers,individual selected and/or tuned to have optimal characteristics in alimited wavelength region, can provide spectroscopic analyses that arebeyond capability of a single spectrometer system.

Analysis of a sample site by optical emission spectroscopy of theablation plasma plume also can be limited by inherent characteristics ofthe plasma plume itself. For example, continuum emission can obscurecharacteristic spectral lines emanating from the ablated material from asample site. As already disclosed above, continuum interference can bediminished and/or eliminated by using a high-speed detector that isgated to exclusively detect line emission during a time interval aftercontinuum intensity has decayed. Nevertheless, there are also inherentlimitations arising from spectral overlap, interference, broadening,and/or low emission intensity at certain characteristic wavelengths,that remain difficult and/or impractical to overcome. Emission spectraanalysis has some limitations can be traversed by applying a differentspectral technology. For example, an ICP-MS can perform elemental and/orisotopic composition analyses at material concentrations well below 500ppb, or even less than 1 ppb, that are inaccessible using emissionspectroscopy alone. In various embodiments with respect to FIG. 8simultaneous analysis of gaseous species from a sample site using ICP-MScan provide complementary ion mass to charge ratio peak intensityanalytical information. In various embodiments, computer 8710 hasanalytical software operable to determine the composition of a samplesite based on the spectroscopic data from plasma plume emission and theICP-MS ion mass/charge ratio intensity data as a whole. It is found thatthe analysis based on LIBS optical emission spectroscopy and ICP-MS ionmass/charge ratio peak intensity data as a whole can detect far moreelements, and can have greater analytical accuracy relative to LIBSemission spectroscopy or ICP-MS alone.

A multi-spectrometer system such as disclosed relative to FIGS. 8-11 canhave use different types of optical spectrometers and detectors at thesame time to advantage. Some embodiments comprise a scanning CzernyTurner spectrometer (CZ) coupled to an ICCD detector. This combinationcan effectuate extremely high sensitivity owing to maximal lightthroughput to the ICCD (high efficiency) from the spectrometer, and ICCDcapability to amplify weak signals in the detector. Accordingly, it isadvantageous where the highest possible sensitivity is needed to detectnumerous different elements present in the range of 1 to 10 parts permillion. However, this combination has the disadvantage that it can onlycapture a relatively narrow range of preselected wavelengths with apredetermined spectral resolution. Furthermore, the wavelength range andresolution vary inversely. The higher the spectral resolution, thenarrower the range of wavelengths that can be covered at one time.Accordingly, to capture high resolution spectral information from atomicelements having spectral emissions in widely separated wavelengthregions using only one CZ-ICCD, the CZ must be sequentially reconfiguredto access each of the separated wavelength regions, and an additionalablation of the sample site must be performed after each reconfigurationto generate the spectral emissions for capture.

An embodiment may also include an Echelle spectrometer coupled to anICCD detector. This combination has the advantageous capability of beingable to capture a broad range of wavelengths at one time in emissionfrom the plasma plume arising from a single ablation (a typical range is200 nm-900 nm, although in a preferred embodiment the range is 190nm-1040 nm and it can be greater). On the other hand, an Echellespectrometer generally has low light throughput (low efficiency). Forexample, an Echelle spectrometer can typically have f/10 aperture lightthroughput whereas a typical CZ spectrometer generally has aboutthroughput in the range of f/3 to f/4. It can be seen that anEchelle-ICCD system is insensitive by comparison to the CZ-ICCD.

Accordingly, some embodiments comprise a plurality of CZ-ICCDspectrometers wherein each spectrometer is configured to receive adifferent preselected wavelength range. The plurality of spectrometersas a whole can capture a broad range of wavelengths at one time yet havevery high sensitivity and resolution. The wavelength ranges can becontiguous and/or can be separated. Furthermore, various wavelengthranges can be non-overlapping or can have overlapping segments. All ofthe spectrometers can receive a portion of spectral emission a plasmaplume simultaneously from one collection optics module through a splitend fiber optic lightguide (described above with respect to FIGS. 10-11), and/or at least some of the spectrometers can receive equal portionsof luminous energy from a dedicated of collection optic module as shownwith respect to FIGS. 9, 11, and 12-13 . One or several of thesespectrometers can include a transmission grating operable to provideenhanced sensitivity in the red and near-infrared spectral region.

Some further embodiments comprise an array of Czerny Turner-CCD opticalspectrometers (e.g. each comprising a Czerny Turner monochromator with aCCD detector). Each spectrometer covers a preselected, non-overlapping,wavelength region. The array of spectrometers is operable to acquirespectral data synchronously from each ablation. The embodiments have anadvantage of being able to capture broadband spectral information in awide range of wavelengths. For example, an operable range of wavelengthscan be 190 nm-1040 nm, although a narrower range can be preferable forgreater resolution, depending on the application. In some embodimentsthere can be overlapping spectrometer wavelength regions. A partiallyoverlapping wavelength region can be useful to calibrate the response ofthe different spectrometers regions with respect to one another usingregions of overlap.

The various detectors and monochromators/spectrometers have advantagesand disadvantages with respect to one another. For example, while a CCDdetector is generally less sensitivity than an ICCD, CCD technology isrelatively inexpensive in comparison to an ICCD having an equivalentnumber of channels. A CCD detector is well suited for broadbandanalysis. Besides having less sensitivity, another limitation of CCDdetector arrays is that they cannot be gated on and off in very shortintervals to discriminate against continuum emission and/or otherinterference.

In the analysis of unknown samples, a broadband CCD spectrometer and/orarray of spectrometers can be first used to survey the principalelements that are present, and identify the elements present inmajority, minor, and/or trace concentration levels. After a sample ischaracterized using a broadband optical spectrometer (such as onecomprising a CZ-ICCD or CZ-CCD combination), higher resolution lowerintensity spectral data obtained from a high resolution, lowersensitivity spectrometer and/or plurality of high resolution/highsensitivity spectrometers in an array can be provide trace elementanalysis. As disclosed above, various embodiments can acquire bothbroadband and low intensity, high resolution spectroscopic data from asingle ablation plume simultaneously.

In some embodiments, the sample may be in a solid phase or a liquidphase (i.e., the sample may be condensed matter). In some embodiments,the sample may be in a gas phase. In some embodiments, the sample may bean aerosol; an aerosol is a suspension of fine solid particles or liquiddroplets in a gas.

In some embodiments an apparatus includes a laser, a sample holder, anemission collection system, and a spectrometer. The sample holder isconfigured to hold a sample. The laser is configured to apply laserenergy to the sample and generate a plasma 220. The emission collectionsystem is configured to collect optical or electromagnetic emissionsfrom the plasma 220 that may then be input to the spectrometer.

In some embodiments, the spectrometer may be operable to detectelectromagnetic radiation of a wavelength of about 200 nanometers (nm)to 900 nm. For example, the spectrometer may be operable to detectintensity and wavelength values of the electromagnetic radiation. Insome embodiments, the emission collection system may include collectionoptics configured to receive light from the plasma and a fiber opticcable operable to transmit the light from the collection optics to thespectrometer. In some embodiments, a detector that is included as partof the spectrometer may include an intensified charge coupled device(ICCD), a charge-coupled device (CCD), or a photomultiplier tube (PMT).

There are some embodiments where a method may be performed with theapparatus 200. A laser energy is applied to a region of a sample with alaser to generate a plasma. In some embodiments, the sample may be in asolid phase, a liquid phase, or a gas phase. In some embodiments, thesample may be an aerosol. A spectrum generated by a plurality ofmolecular species in the plasma is recorded with a spectrometer or otherdevice. For example, with the apparatus 200, the ablation laser may beused to generate a plasma from the sample, and the emission collectionsystem and the spectrometer may be used to record the spectrum generatedby the plurality of molecular species. The spectrometer may detectelectromagnetic information (e.g., light) generated by the plasma.

In some embodiments, the laser energy may be applied to the region ofthe sample in a pulse of laser energy. Any laser wavelength, laserenergy, and laser pulse width may be used to generate a plasma. In someembodiments, the laser wavelength may be about 1064 nanometers (nm), thelaser energy may be about 50 millijoules (mJ) to 100 mJ, and the laserpulse width may be about 4 nanoseconds (ns). For example, a neodymiumdoped yttrium aluminum garnet (Nd:YAG) laser may be used to generateenergy in the near infrared region of the electromagnetic spectrum witha wavelength of 1064 nm. With a pulse duration of about 4 ns, a laserbeam with a power density of greater than one GW/cm2 at the laser beamfocal point can be formed. In some embodiments, the pulse duration canbe decreased to femtoseconds. In some embodiments, the laser beam can befocused to a spot size of about 10 micrometers to 500 micrometers, orabout 150 micrometers to 200 micrometers.

Some embodiments may include ablating the sample with the applied laserenergy. Such a process may be referred to as laser ablation or ablation.

Further embodiments may include vaporizing the sample with the appliedlaser energy. Other embodiments may include desorbing the sample withthe applied laser energy. Some embodiments include vaporizing the sampleor desorbing the sample with the applied laser energy, a plasma may notbe formed with the applied laser energy. In these embodiments, themethod may further include imparting additional energy to the vaporizedor desorbed sample to form a plasma including the plurality of molecularspecies.

In some embodiments, additional energy may be imparted to the plasma.The additional energy may cause molecular species in the plasma toproduce additional optical or electromagnetic emissions that can bedetected with the spectrometer. In some embodiments, such additionalenergy may be imparted to the plasma in a microwave field or a radiofrequency (RF) field. In some embodiments, such additional energy may beimparted to the plasma with an additional pulse of laser energy. Forexample, there are some embodiments that may include applying a firstpulse of laser energy at a first angle with respect to the sample, andthen applying a second pulse of laser energy at a second angle withrespect to the first angle. In some embodiments, the second angle may beabout 0 degrees to 90 degrees with respect to the first angle.

The plasma may include ionic, atomic, and molecular species. In someembodiments, the plasma, immediately after application of the laserenergy may include a molecular species or a plurality of molecularspecies. In some embodiments, species atomized from the sample may reactwith each other to form a molecular species or a plurality of molecularspecies. The molecular species may include diatoms (e.g., Na₂, C₂) orexcimers (e.g., He₂, Xe₂, and XeCl), for example.

In some embodiments, the plasma may be allowed to react with species inthe surrounding environment to form a molecular species. For example,operation may be performed in ambient air under ambient pressure.Species in the plasma may react with oxygen or nitrogen, for example, inthe air to form oxide molecular species or nitride molecular species,respectively. Whether the as-formed plasma includes molecular speciesdepends in-part on the laser wavelength, the laser pulse duration, thelaser power, the laser spot size, and the laser fluence. When the plasmais allowed to react with species in the surrounding environment to forma molecular species, the time needed for such a reaction or reactionsalso depends in-part on the laser wavelength, the laser pulse duration,the laser power, the laser spot size, the laser fluence, the sample, andthe molecular species.

In some embodiments, a period of time between operations is set orspecified to increase or maximize the intensity of molecular emissionand to decrease or minimize atomic emission and ionic emission (i.e.,emission from atoms and atomic ions). Again, this period of time dependsin part on the laser wavelength, the laser pulse duration, the laserpower, the laser spot size, the laser fluence, the sample, and themolecular species.

As noted above, optical or other electromagnetic emission generated bythe plasma may be recorded by a spectrometer or other device. Someembodiments include recording the spectrum with visible spectroscopy,recording the spectrum with ultraviolet spectroscopy, recording thespectrum with infrared spectroscopy, or recording the spectrum withnear-infrared spectroscopy. Some embodiments include recording directoptical emission of the plurality of molecular species, recordingoptical absorption of the plurality of molecular species, recordinginduced fluorescence of the plurality of molecular species, recordingRaman scattering of the plurality of molecular species, recordingluminescence of the plurality of molecular species, recordingphosphorescence of the plurality of molecular species, recordingphotoacoustics of the plurality of molecular species, or recordingphotoionization of the plurality of molecular species.

In some embodiments, the method may be performed more than once or aplurality of times on the same region of the sample. The recordedspectrum for each repetition of the method may then be averaged. Forexample, in some embodiments, the method may be repeated two times orthree times on a region of a sample. Performing the method on the sameregion of the sample multiple times and averaging the results may yielda spectrum with less noise and less experimental error.

A chamber may contain a specific gas or gasses at a specific pressure orpressures. The gas or gasses may be specified, depending on the samplebeing analyzed, such that desired molecular species may be formed thataid in quantifying the abundance of isotopes in the sample. For example,a gas may be selected such that the spectra formed by two molecules,each including a different isotope of an element, in the sample have anisotopic spectral shift that is able to be resolved by the spectrometerbeing used. Further, the sample inside the chamber may be held at aspecific temperature. When a sample is held at one temperature versus adifferent temperature, different molecular species may be formed in theplasma. Using such an apparatus 700, some control over molecular speciesformed when the plasma reacts with the environment may be achieved;i.e., by controlling the plasma properties, the formation of specificmolecules can be controlled.

Some embodiments, to control the gas or gases with which the plasma mayreact, the chamber may be operable without a chamber. In some of theseembodiments, tubes or other devices may be used to deliver a gas to theregion where the plasma is to be formed.

In some embodiments, laser energy is applied to a region of a samplewith a laser to generate a plasma. The plasma generated may be generatedin a chamber of the apparatus. The chamber may contain a specific gas orgasses at a specific pressure or pressures. A spectrum generated by aplurality of molecular species in the plasma is recorded with aspectrometer or other device.

Liquid and Solid Sample Analysis

A compact portable LIBS apparatus, capable of analyzing the elementalcomposition of any liquid or solid samples in real time without anysample preparation or transformation is disclosed. The disclosed LIBSinstrument can be used as a universal elemental analyzer owing to itscapability of analyzing plurality of sample states and materialstructures. Furthermore, it can be conveniently transported to differentlocations as needed owing to relatively small size. The suction hose andthe power cables of the LIBS apparatus can be easily detached fortransportation. Several instruments dedicated to analyze only onespecific form of a sample can be replaced by the universal elementalanalyzer. Thereby the disclosed LIBS apparatus and methods can improveprocess efficiency, cost, and space use. The disclosed methods includegeneration of aerosols from liquid samples operable to measure elementalcomposition, focusing and confining preselected laser beam to theaerosol using optical elements, ablating a stream of the aerosol togenerate a plasma plume, collecting and gathering lights from the plasmaplume, monitoring and analyzing optical spectra emitted by laser-inducedplasma, and real time analysis of optical emission from the plasmaplumes to detect and quantify elements. Furthermore, LIBS describedherein provides a rapid chemical analysis of a plurality of sampleswithout any requirement of consumables and/or generation of acidic wasteas compared to other methods for elemental detection in the prior art.

Various embodiments of a multiphase laser ablation analysis instrumentaccording to the instant disclosure, can effectuate quantitativeelemental analyses of liquids and solids having a very wide range ofphysical characteristics and chemical compositions. For example,virtually any liquid such as petroleum, light and heavy fuels, liquidfood products, and solvents, and/or solid samples such as rocks,batteries, solid chemical reagents, and others having homogenous and/orheterogenous material structure and compositions be analyzed.

FIG. 14A shows a schematic diagram of a LIBS apparatus and optical pathsof a laser beam for analysis of a liquid phase or a solid phase samplein an illustrative embodiment according to the present disclosure. TheLIBS technology for analysis of liquid and solid sample described hereincomprises a liquid sample introduction system which can include a pump,a nebulizer, a gas carrier, and a spray chamber, a solid sample stageoperable to move in x, y, z axes independently, a single pulsable laserwith various optical elements to create a plasma plume from both liquidand solid sample material, an exhaust system, light gathering andtransmitting elements (which can include fiber optics, lenses, mirrorsand various other components described above), a spectrometer with adetector, computer software and/or firmware operable to perform realtime data analysis, and various control loops operable to automateoperations with no human interaction.

As shown in FIG. 14A, the portion of LIBS for liquid sample materialanalysis has a compact pump D10, preferably peristaltic pump, whichdelivers a liquid sample into a nebulizer D20 with a preselected flowrate depending on the characteristics of the liquid sample. The cyclesof the peristaltic pump can be synchronized with the laser to optimizeprocess efficiency. A pressurized carrier gas D30 flows into thenebulizer D20 where a portion of a liquid sample was aerosolized into astream of fine and preferably uniform aerosol particles. The nebulizercan be pneumatic (cross-flow, concentric, Babington type, V-groove,parallel-path, flow-blurring, micro-flow or self-aspirating, etc.)and/or ultrasonic. The pneumatic nebulizers require a flow of a carriergas D30 which can be an inert gas such as nitrogen, argon and others.The self-aspirating pneumatic nebulizers do not require a peristalticpump. The nebulizer can be pulsed, and the pulsed nebulizer can besynchronized with the laser used for LIBS analysis. Alternatively, anynozzle, electrospray, any other types of liquid aerosolizer, and/or amist dispenser can be used to generate a stream of aerosol D45 with apreselected size distribution depending on the application. Anillustrative embodiment shown in FIG. 14A includes a cyclonic spraychamber D40 that is used to remove large droplets produced occasionallyby the nebulizer. A Scott double-pass type of a spray chamber can beused alternatively to remove large droplets from the aerosol steam. Theunused portion of the aerosol stream can be suctioned away by a pumphaving air purification filters such as an activated carbon, HEPA,ASHRAE, any combination thereof, and/or others connected to a suctionfunnel D50 as shown in FIG. 14A. Unused liquid sample can be drawn offinto a recycling or waste bottle.

A LIBS system for liquid or solid sample analysis can have a pulsedlaser D110 shown in FIG. 14A having various power, pulse, wavelengthcharacteristics in different embodiments. The laser can be a solid stateNd:YAG and/or an excimer gas laser. The laser pulse energy can rangefrom tens microjoule to hundreds millijoule. The laser pulse repetitionrate can change from single shot to several kilohertz. The laser can bea nanosecond or picosecond pulsed laser with a fixed spectral wavelengthranging from ultraviolet to near-infrared.

An example of a laser beam delivery scheme before reaching a solid phasesample site or a laser focal point in an analysis zone filled withflowing aerosol stream produced from a liquid phase sample is shown inFIG. 14A for LIBS analysis. The laser D110 in some embodiment canoperate exclusively at a fundamental frequency or variable frequenciesincluding a higher harmonic generator for operation on amultiplicative-integer frequency. Some embodiments can include anattenuator D120 to control laser power from 0% to 100%. Furtherembodiments can include two flat mirrors D130, D140 to effectuate acompact arrangement of the LIBS apparatus. Two flat mirrors D170, D180can be installed at a fixed low angle of incidence that causes an inputlaser beam to undergo multiple reflections to produce a laser beam withan approximately Gaussian amplitude profile D60. A Gaussian beam profileis generally an optimal profile for generating plasma in an aerosolstream because it can be focused tightly and therefore can produce ahighly energetic plasma. For example, a beam can enter a two flat mirrorsystem such as D170 and D180 configured to reflect the laser beam 4times at each mirror surface, before exiting the two-mirror system andreaching to a preselected position in an analysis zone D48 filled byflowing aerosol stream D45 generated from a portion of a liquid samplematerial.

A Gaussian-shaped laser beam D60 described above can be further focusedby a lens D70 illustrated in FIG. 14A and/or a combination of lenses.One preferable embodiment has a combination of a plano-convex lens witha positive meniscus lens which directs the laser beam in a preselectedposition. A mirror or a mirror system is preferably used as a focusingelement since it does not cause chromatic aberrations. Furthermore,using mirrors instead of lenses facilitates the full spectrum collectionwithout significant losses of efficiency in the ultraviolet andnear-infrared regions of a recorded spectrum. The laser beam is focusedinto the preselected laser focal point D47 in analysis zone D48including a stream of sample aerosol D45 produced by nebulizer D20 andspray chamber D40. The optical emission generated by the laser-inducedplasma is collected by a curved mirror D80, preferably a concavespherical mirror. Alternatively, a system of two off-axis parabolicmirrors, or an objective lens, a combination of lenses and/or mirrorscan be used to collect optical emission generated by the plasma plume.The optical emission from a laser-induced plasma is focused into anoptical fiber D90 which can be coupled to an optical spectrometer D100.Alternatively, an objective lens, a combination of lenses and/or mirrorscan be used to deliver the optical emission into an opticalspectrometer. The optical spectrometer is fitted with an opticaldetector. In one preferred embodiment the optical detector can be gated.The parameters of the laser pulses and the gating of the opticaldetector can be cooperatively optimized to effectuate high sensitivityand/or accuracy in the chemical analysis.

In further embodiments, a movable mirror D150 shown in FIG. 14B candirect a laser beam toward a beam homogenizer D160. Mirror D150 can beplaner, concave, convex and/or parabolic depending on the applications.Mirror D150 can be rotated and/or translated to a preselected position.The beam homogenizer smooths the irregularities at the edge of a laserbeam and creates a beam with a uniform energy profile. It can also beused to adjust the laser spot size at the sample surface. To generate abeam with a uniform energy, the beam homogenizer can transform an outputlaser beam into a far-field collimated beam using a circularcross-section of approximately uniform irradiance at the focal plane.The cross-section of uniform irradiance can be linear, square, or of anyother geometric shape. A collimated beam is parallel rays of lighttherefore has relatively uniform intensity and/or energy profile andspreads minimally as it propagates. Collimated beam D190 with uniformintensity profile, also called as a flat-top or top-hat laser beam, canbe directed to the surface of a solid sample located in a chamber. Insome embodiments, additional flat mirrors can be installed to facilitatethe steering of a beam within a compact arrangement of the instrument.This flat-top laser beam distribution is critical for precise andaccurate chemical analysis of solid phase samples.

A collimated flat-top laser beam D190 with an adjustable circularcross-section is directed toward an optical objective D230 preferably anapochromatic objective with a long working distance and a minimum ofaberrations. In various embodiments, a flat mirror D220 facilitates acompact physical arrangement of the instrument. In some embodiments themirror D220 can be a dielectric coated mirror that is highly reflectiveon the laser wavelength but is transparent to all other lightwavelengths. A laser beam can be focused on the surface of a solidsample D240 placed into a sample chamber D250. The sample chamber canhave a transparent window, through which a collimated laser beam passesperpendicularly for sample ablation. The sample chamber can be installedon a precisely movable stage D260 coupled to x-y-z translation motorsthat are operable to move the sample chamber on the stage in x, y, zaxes independently. The size of the translation stages can range fromseveral tens to several hundred millimeters. The stage typically canmove in each direction with linear resolution less than 1 micrometer. Asample chamber can have different configurations to secure the sample.It can be non-sealed, marginally sealed such as sealing with a rubberband, or rigorously sealed to allow the analysis of sensitive and/orhazardous materials (for example, Li-ion battery or radioactivematerials) in an enclosed environment. A sample chamber may include aremovable spacer D270 to analyze samples with very small dimensionsconveniently. The spacer can be move back and forth to accommodatedifferent sample dimensions. To optimize the analysis of various samplesizes further and reduce the amount of unused volume in the samplechamber, spacers in different sizes having corresponding sizes can beprovided. The stage with the sample chamber can precisely move thesample in a predetermined pattern relative to the laser beam ablationspot, thereby systematically ablating the selected sites of the sampleto obtain a composition map of the sample. The composition map cancomprise an elemental analysis of one or more sample sites. Laserablation of the solid sample surface removes a portion of material at aselected sample site and creates a depth of the ablation cratersdepending on the power of the laser. A serial ablation of the sample byrefocusing the laser to the depth of the ablation crater effectuates alayer-by-layer analysis, thereby generating a 3D image of the samplechemical composition.

Characteristic spectral emission emanating from a LIBS plasma plumegenerated by ablation of solid phase sample material is collected at alow angle relative to the incident laser beam by an objective D280 andtransmitted through an optical fiber cable D90 to an opticalspectrometer D290. Optical spectrometer D290 and optical spectrometerD100 in FIG. 14A can be same or different. In some embodiments, two ormore objectives D280 can be installed symmetrically in a circle around alaser beam objective D230. The later arrangement is particularly usefulwhen an optical spectrometer D290 is a multi-channel configuration ofseveral spectrometers. In one embodiment, each spectrometer channel canbe coupled to its own optical objective D280. In further embodiments, atleast a channel for ultraviolet light is coupled to a dedicatedultraviolet objective, and the other channels for visible to nearinfrared light are coupled to the second objective. Chromaticaberrations are substantially reduced in a configuration having multiplededicated objectives. The laser beam focusing and light collectionoptics can include additional optical elements depending on theembodiments.

The laser breakdown beam is focused to a spot below the focusingobjective D230 for solid sample analysis. Translation stage D260 canmove a preselected sample site to the laser spot position to ablatematerial from the preselected sample site. The distance from thefocusing objective D230 to the surface of sample D240 in chamber D250can be measured using triangulation sensor D300 shown in FIG. 14A.Further, sample D240 in chamber D250 can be moved by stage D260 in apredetermined pattern precisely and automatically to generate a chemicalimage of the ablated area of a solid sample. One-, two-, orthree-dimensional chemical image of a solid sample can be measured. Insome embodiments flat mirror D310 and compact CMOS camera D320 providemagnified images of the sample surface for visual inspection andnavigation.

Sample chamber D250 includes several miniature light emitting diodesD330, D340 for even and adjustable flood illumination of the sample. Asample chamber can have an inlet and outlet D350, D360 to admit andexhaust a flow of unreactive gas and/or air through the chamber. Theunreactive gas can be an inert gas such as nitrogen, argon, or heliumwhich can come from a cylinder D370. The flow rate of gas from thecylinder can be controlled using a mass flow controller D380. The choiceof a carrier gas depends on the sample and element(s) planned to bemeasured. For example, an argon atmosphere facilitates opticalexcitation of metal and other atoms providing a stronger signal in LIBSmeasurements. On the other hand, a helium atmosphere facilitates opticalexcitation of halogen and other non-metal atoms. In an embodiment, asample chamber can include also lights on the bottom of the chamber toilluminate transparent samples. In some embodiments, the temperature ofa sample chamber can be adjusted depending on the characteristics of thesample. It can be heated using an electrical resistance heater and/orcan be cooled using a refrigeration coupled to an exchanger, athermoelectric cooler, and/or a phase change medium such as ice water tooptimize the LIBS signal. Furthermore, the sample chamber canaccommodate multiple samples at the same time which increases theefficiency of loading samples to the instrument.

FIG. 14B is a simplified diagram of a portion of apparatus showing abeam emanating from a laser and optical elements to direct and/or focusthe laser beam to form an emissive plasma from an aerosolized liquidsample or a solid sample, according to an embodiment. A pulsed laserD110 generates a laser beam that passes through an optical attenuatorD120 toward a flat mirror D130. The flat mirror D130 reflects a laserbeam perpendicularly toward a precisely movable mirror D150. Whenmovable mirror D150 is in position D152, the laser beam can be reflectedin an optical path including a negative lens D390. The negative lensD390 in cooperation with a positive lens D400 can expand the laser beamdiameter. The expanded laser beam passes through diaphragm apertureD410. Aperture D410 is configured to pass only the central part of thelaser beam having an approximately uniform radial intensity profile. Therelatively uniform laser beam produced thereby is directed along anoptical path to a solid sample chamber to produce a plasma plume forLIBS analysis. The size of a laser spot generated at a sample site canbe in the range of 10 μm to 200 μm or sometimes even larger. In otherposition D151 of the movable mirror D150, the laser beam from a flatmirror D130 passes to another flat mirror D140 shown in FIGS. 14A and BThe second flat mirror D140 reflects a laser beam perpendicularly towarda system of two flat mirrors D170, D180 as shown in FIG. 14A to producea laser beam with an approximately Gaussian intensity profile. The laserbeam with an approximately Gaussian intensity profile is directed towardliquid sample analysis.

The diagrams in FIGS. 14A and 14B are the illustrative examples showingvarious practical embodiments of the present disclosure. In variousembodiments, a collimated flat-top laser beam, a Gaussian beam, and/orother laser beam profiles can be formed and used for analysis ofdifferent solid or liquid phase sample materials depending on theapplication. In a number of embodiments, different lasers types, opticalelements, optical spectrometers, detectors, other components of the LIBScan be used interchangeably to optimize LIBS signals further.

In an embodiment, a compact pump can be used to introduce a portion ofliquid sample into a nebulizer operable to aerosolize liquid samplematerial into a stream of carrier gas. The liquid sample aerosol flowsthrough nozzle D41 emerging in aerosol stream region D45. Mirror D150 ismoved into non-intercepting position D151 to allow laser pulsesemanating from single laser D110 to follow an optical path D60 to afocal point D47 in analysis zone D48 within the flowing aerosol streamD45. The laser pulses produce an emissive plasma plume surrounding thefocal point comprising liquid sample material. The optical spectrumemanating from the plasma plume generated by the laser ablation can bemeasured with a spectrometer. The liquid samples can be any aqueous andnon-aqueous solutions including as waste water, beverages, urine,solvents, kerosene, gasoline, diesel, biofuels, mineral oil and crudepetroleum samples, and others. Both univariate and multivariatecalibrations can used to quantify the spectroscopic sample measurementsusing known reference standards.

The sensitivity of the LIBS analyses obtained using apparatus andmethods disclosed herein met or exceeded American Society for Testingand Materials (ASTM) standard method D5185 for multi-element ICP-OESanalysis of lubricating oils. In general lower limits of detection forthe present methods and apparatus for elements tested were also foundmeet or exceed the requirements of ASTM standard method D5185 which ishereby incorporated by reference in its entirety (ASTM Volume 05.02Petroleum Products, Liquid Fuels, and Lubricants (II): D4177-D6468, ASTMInternational, 2020).

Clean or used motor oil from a variety of vendors such as diesel fuels,PremiSolv solvent (odorless proxy to kerosene), and fuel additives(lubricants, boosters, inhibitors) were also analyzed using the LIBSapparatus and methods disclosed herein. The minor elements found in thepetroleum products tested according to our liquid LIBS methods disclosedherein included Ca, Mg, V, and Na indicating that these productscontaminated with particulate matter likely caused by metal wear. Thesmall particulates were readily atomized, measured and quantified usingthe apparatus and methods based on LIBS. The limits of detection definedby tripled standard deviation in spectra of blank sample (3σ) formetallic contaminants were estimated to be around “single-digit” ppm(mg/kg). A person having ordinary skills in the art would appreciatethat small particulates in a liquid sample may be insoluble and/ordifficult to atomize using ICP plasma.

100 laser pulses with 10 Hz frequency were used in a typical trial toform luminous plume(s) for measuring each chemical element spectra withan analysis time of 10 sec. The spectra from the laser plumes were usedto calculate the relative standard deviations of the measurements, toconstruct linear calibrations for each element, and to determine 3σlimits of detection and triple standard deviations of a blank sample.The results of these measurements are summarized in table in FIG. 15that shows the detection limits of the elements tested using LIBS inargon and nitrogen flows and the lower limits of detection specified inthe ASTM standard test method D5185 for ICP-OES analysis of lubricatingoils. As shown in the table in FIG. 15 , considerably smallerconcentrations of most elements tested were detected using present LIBSapparatus embodiment in an argon flow as compared to those using thestandard test method for ICP-OES. Furthermore, the detection limitsusing instant LIBS in a nitrogen flow also met or exceed for someelements (V, K, Na, Li, Fe, Mg) as compared to those performed in theargon flow tests.

The table in FIG. 15 shows the lower limits of detection of analytetrace elements tested using present LIBS methods and apparatus indifferent carrier gas and/or solvents in comparison to the limits ofdetection specified in the ASTM test method D5185 for ICP-OES analysisperformed in tenfold diluted lubricating oils and nebulized by argoncarrier gas. The limits of detection by present LIBS for aqueoussolutions in argon flow shown the column 3 in the table obtained by LIBSinstrument configured with a 6-channel spectrometer, and measuringbroadband spectra from 1000 laser pulses on CCD detectors. Column 4shows the limits of detection of the elements in Conostan base oil (a)directly nebulized in argon flow using LIBS instrument configured with acompact Czerny-Turner spectrometer and ICCD camera, and accumulatingspectra from 100 laser pulses. Column 5 demonstrates the limits ofdetection in base oil (b) measured in the same configuration as Column 4but using nitrogen flow as a carrier gas. Column 6 shows the limits ofdetection in base oil (c) measured in a similar configuration as Column5 but using a compact Czerny-Turner spectrometer and ICCD camera from adifferent vendor. The latter configuration of present LIBS, the limitsof detection for aqueous solutions nebulized in nitrogen flow that areorder of magnitude lower than the records shown in Column 3.

The National Institute of Standards and Technology (NIST) referencematerials such as Vanadium in Venezuelan Crude Oil (RM-8505) and TraceElements in Fuel Oil ‘No. 6’ (SRM-1634c) were analyzed for traces ofvanadium to evaluate the performance of instant LIBS apparatus andmethods. Vanadium concentration in Venezuelan crude is specified to beabout 390 ppm (mg/kg) and a certified mass fraction of vanadium in FuelOil ‘No. 6’ is only 28.19±0.40 ppm (mg/kg). NIST reference materials forboth of these levels were successfully measured using a LIBS apparatusembodiment as shown in FIG. 16 . The spectra of Venezuelan Crude Oil F10and Trace Elements in Fuel Oil No. 6 F20 after background subtractionfor the region of the most prominent ionic quintet of vanadium spectrallines are shown in FIG. 16 . The most intense emission line in thisquintet was observed at 309.31 nm. The background emission in thisspectral interval comprises continuum bremsstrahlung radiation fromplasma electrons and molecular transitions of free radicals OH and CH.The CH emission originates from the oil matrix but it does not directlyinterfere with the vanadium spectral lines. The OH emission originatesfrom the water content in oil and humidity of the ambient air. The OHspectrum in this region has many partially-resolved rotational linesthat should be subtracted or at least accounted as a possibleinterference.

The ability of a LIBS apparatus embodiment to perform multi-purposeanalyses of all kinds of the petroleum-related liquid samples wasdemonstrated with especially good sensitivity for traces of metals.Optical emission from major, minor and trace elements in various sampleswas detected, measured and quantified. For example, metal signals fromsamples of Conostan base oil standards (kinematic viscosity 20 and 75cm²/s, cSt), mineral paraffin oil, Arabian, Azerbaijani, Texan and algaecrude oils, lubricants, fresh and used motor oils were measured.Elemental quantification of the LIBS data was done with standardunivariate calibration using an area under a spectral line contourfitted by Lorentzian profile.

To investigate the utility of LIBS ability for analyzing the lightestdistillation fractions, the samples of methanol, ethanol, acetone,ortho-xylene, isopropanol, isooctane, gasoline, methyl isobutyl ketone,water and aqueous solutions were nebulized, ablated and the signals fromthe aerosolized samples were measured. For example, FIG. 17 shows theLIBS spectra of Mg ionic emission at 279.55 nm from the gasoline sampleG70 and the calibration standards prepared using PremiSolv (Conostan, aDivision of SCP SCIENCE) as a pure source with known concentrations ofmagnesium (0 ppm Mg G10, 0.05 ppm Mg G20, 0.1 ppm Mg G30, 0.5 ppm MgG40, and 1 ppm Mg G50). The concentration of Mg in a gasoline sampleobtained from a regular gas station was about 10-fold higher than thelimit of detection of the LIBS instrument shown in FIG. 17 .

The hydrogen-to-carbon (H/C) ratio is an important parameter forpetroleum characterization since the quality of a petroleum cut(fraction) generally increases with the H/C ratio. The greater the H/Cratio, the greater the amount of energy that can be released whenpetroleum fuel undergoes combustion. The H/C ratios also correlate withthe aromaticity indexes and specific gravity of hydrocarbons. A personhaving ordinary skills in the art would appreciate that thesemeasurements cannot be performed using conventional inductively coupledplasma (ICP) or x-ray fluorescent (XRF) analysis in a single instrumentand/or in combination.

Quantitative calibration for determination of the elemental H/C and 0/Cratios in solvents using the broadband LIBS spectra was successfullyperformed using the present LIBS methods.

Organic solvents namely ethanol, methanol, ortho-xylene, and theirmixtures were chosen to investigate the ability of LIBS to measure theH/C ratio in liquid samples. These solvents have very different ratios:The H/C for methanol is 4 and the H/C for ortho-xylene is 1.25. Themixtures of methanol and ortho-xylene yield intermediate H/C ratios. Anembodiment equipped with a compact 6-channel spectrometer having CCDdetectors was used for rapid acquisition of the broadband spectra ofthese samples. Undiluted ortho-xylene samples exhibited the highestintensity of molecular emission from CN and C2 radicals since theortho-xylene molecule has an aromatic ring with conjugated double bonds.A methanol molecule does not have double carbon bonds. Consistent withthis, the LIBS spectrum of aspirated methanol exhibited only weakemission at the Swan bands of C2. The recorded spectra imply that theintensity of molecular emission of CN and C2 radicals can be associatedwith the molecular structure of an interrogated sample.

Quantitative calibration plots were constructed to determine the H/Cratio in solvents with the acquired broadband spectra. A person havingordinary skill in the art would appreciate that non-linearity of thecalibration plots impeded determination of the H/C ratio. Suchnon-linearity problems was overcome using the entire broadband spectra(190-1000 nm) for multivariate calibration based on partial leastsquares regression. Using conventional instruments, it is difficult toacquire such broadband spectra. An exemplary multivariate partial leastsquares regression for calibration of the C/H ratio measurement usinginstant LIBS instrument is shown in FIG. 18 .

Separation of an unknown samples requires laborious manual orsemi-manual spectral examination using conventional techniques. On theother hand, unknown samples can be easily separated using instant LIBSembodiments. The chemometric data of the LIBS spectra were processedusing principle component analysis (PCA). For example, FIG. 19 shows aclear separation of gasoline I40, ethanol I30, and two mineral oilsamples (25 cSt I10 and 75 cSt I20) in principal component space afterstatistical analysis.

In various embodiments, principal component analysis (PCA) and partialleast squares regression (PLSR) are embedded in the data analysissoftware in an embodiment, and operate cooperatively to effectuatesimple statistical algorithms that provide quantitative analyses.

The argon flow was used to facilitate comparison between the performanceof instant LIBS apparatus and methods and conventional ICP-OES analyses.The ICP technique uses an inductive plasma sustained in flowing argon.Another reason for using argon is that when laser ablation is performedin an argon atmosphere, relatively more intense emission is obtainedcompared to other common gas media. Nitrogen was also tested as acarrier gas for analysis of Conostan oil standards (NIST traceable) andvarious crude oil samples. The net emission signal in argon was higherthan the signal in nitrogen, but the continuum background and noise innitrogen were found to be lower than in argon. As a result, it was foundthat estimated detection limits for some elements in various embodimentswere lower in nitrogen (offering better detectability) than those doneusing an argon flow. Compressed air was also tested as a carrier gas andwas found to be compatible with various analyses. Although argon flowprovided better detection limits for most elements, the compressed airflow, nonetheless, was found to result in better (lower) detectionlimits for the elements Al, K, Li and Na.

LIBS analysis using nitrogen gas or compressed air as a carrier gasprovided a degree of detectability, sensitivity, and accuracy thatimprove upon ICP-OES using argon flow. Moreover, LIBS does not have thewell-known limitations of ICP. For example, introduction of asubstantial amount of liquid (especially organic) sample into the ICPanalysis region may quench and extinguish the plasma. Furthermore, ICPis burdened by a loss of sensitivity when sample dilution is necessaryto avoid extinguishing of plasma.

The spectra acquired from four motor oil samples of 10W30 grade made byChevron, Shell, Valvoline and Mobil were processed using a partial leastsquare (PLS) algorithm by taking into account the small differences inthe intensities of major spectral features (O, N, H, CN, C2) and thesubstantial differences in trace constituents (additives, impurities)among the samples. Accurate discrimination between new and used motoroil was achieved with a high degree of confidence. This is due to asignificant increase in metal emission originating from metalliccontaminants, mostly particulates, in used oil. Thus, LIBS can improvethe efficiency of monitoring oil and fuel quality as well as the extentof metal wear in vehicular systems and hydraulic equipment. Thechemometric algorithms enabled correct identification and rapidclassification of different oils and fuels without traditional elementalcalibration.

Detection of halogens and trace metals in biofuel products is importantto monitor clean combustion and to prevent corrosion of components whenusing these alternative fuel sources. Certain trace metals inplant-derived biomass are valuable to fermentation in biorefinery, butother trace metals are detrimental. The oxidizing metal ions havesignificant effects on the catalytic oxidation of biomass that can leadto depolymerization of the biomaterials such as starch, cellulose, andlignin.

Using an embodiment, choline emission at 837 nm in oil was measuredusing a helium stream at low pressure. The estimated detection limit wasfound to be 13 ppm. In various tests, the Cl spectral line was on top ofan emission background determined by free-electron continuum(bremsstrahlung radiation) and molecular C2 bands. In helium flow, anemission contribution arising from excimer molecule He2 was also seen.Background emissions were normalized and subtracted using the blank oilsample as a reference. Various embodiments also used Lorentzian fittingand statistical noise rejection to reduce and/or remove backgroundinterferences.

Similar tests demonstrated the detection limit of 250 mg/kg (ppm) forthe chlorine measurement in mineral oil using helium flow at atmosphericpressure. The detection limit for chlorine in water using helium flow atatmospheric pressure was 43 ppm. The ability to measure the chlorinecontent in water is important for analysis of produce and frackingwater.

The leading cause of aviation fuel thermal stability failures is knownto arise from contamination by metal traces. Modern aircraft turbineengines are vulnerable to fouling by contaminants in jet fuels (e.g.,JP-5). This occurs because of thermal degradation and oxidation of thefuel at elevated temperatures (250-300° C.) in the engine. Fuelatomizers have been considered the most critical components because theyhave relatively small diameters, and are generally exposed to relativelyhighest temperatures. It is believed that dissolved oxygen in the fuelis quickly converted to organic naphthanates, and then to hydroperoxideswhich decompose to carbonaceous residue that tends to accumulate on thewalls of orifices. The decomposition process can be catalytic. Thecatalysts for degradation are thought to be Cu and other trace elementssuch as Cd, Zn, Fe, Co, Ni and Pb.

Trace level Cu in aviation turbine fuel can significantly acceleratethermal instability of the fuel, leading to oxidation and production ofdetrimental insoluble deposits in the engine. Metals such as dissolvedCu can degrade the storage stability or thermal stability of theaviation turbine fuel by catalytic action. Cu is believed to be the mostdetrimental of these materials and the contamination can occur duringdistribution from the refinery to an airport. One source ofcontamination common to aircraft carriers is “admiralty metal” used asfittings on fuel hoses on most Navy ships. This material isapproximately 70% Cu and 30% Zn. Contact with an admiralty metal fittingmay cause fuel to be contaminated quickly at some level.

The thermal stability of aviation fuel is often measured by a laboratorydevice called a Jet Fuel Thermal Oxidation Test (JFTOT) analyzer. Themethod used is ASTM D3241 which is hereby incorporated by reference inits entirety (ASTM D3241-20a, Standard Test Method for Thermal OxidationStability of Aviation Turbine Fuels, ASTM International, WestConshohocken, Pa., 2020, www.astm.org) Fuel in this tester is heated to260-275° C., passed through a stainless-steel filter and onto analuminum tube. The test is run for 2 hours; the appearance of thealuminum tube is then evaluated for the pass/fail result. Only a slightdarkening of the tube (0-2) is permitted for a pass. Greater darkening(3-4, Peacock and Abnormal) is considered to be failure. JFTOT tests onfuels containing known amounts of metals reveal that only 0.05 ppm of Cuwill affect the test. Greater than 0.05 ppm Cu will likely result in afailure. Amounts exceeding 0.1 ppm of Cd, Zn, Fe, Co, Ni and Pb willalso negatively affect the JFTOT result.

Necessity for real-time determination of the trace contaminants in fuelsrequires the development of an advanced portable analyzer with sub-ppmto ppb level sensitivity for Cu and other metals. The analyzer shouldperform rapid analysis of fuel as it is delivered to aircraft eithershipboard or at an air field. Presently, Air Force fuel samples withsuspected contamination are collected on site and then shipped to afixed regional laboratory that performs the analysis by ICP-OES orICP-MS. That process can typically take 2-10 days for results dependingon site and international customs. During this transit and analysistime, fuel inventories and fuel servicing equipment are placed in aquality hold status, preventing the ability to support aircraft orground vehicle generation and mission requirements. The multi-dayturnaround delays the aircraft in its mission. In addition, the effectof admiralty metal aboard aircraft carriers may be overlooked entirely.

Aviation jet fuels (JP-5, JP-8), diesel and kerosene are all similarhydrocarbons. JP-5 is a hydrocarbon mixture of C9 to C16 with boilingrange 156-293° C. The composition of JP-5 includes 53% paraffins, 31%cycloparaffins, 16% aromatics, and 0.5% olefins. It is essentiallyrefined kerosene. Boiling temperature of JP-8 jet fuel ranges between175 and 300° C. Diesel fuel consists of refined hydrocarbons, primarily75% saturated alkanes, normal, iso- and cyclo-alkanes and 25% aromaticslike naphthalenes and alkylbenzenes. It includes C10-C15 hydrocarbonshaving a boiling temperature range of 150 to 380° C.

The disclosed LIBS apparatus provided the following limits of detectionin PremiSolv (a proxy for jet fuel) directly nebulized by a pneumaticnebulizer in argon flow using a compact Czerny-Turner spectrometerfitted with an ICCD camera and accumulating spectra from 100 laserpulses: Cu 0.07 mg/kg; Fe 2.4 mg/kg; Mg 0.01 mg/kg; Zn 0.6 mg/kg. Theseresults demonstrated utility of the instant apparatus and methods forrapid analysis of aviation fuel that can be performed directly in thefield.

There has been a long felt need for an advanced analytical measurementtechnology to meet the analytical requirements and provide real-timedetermination of the trace impurities in aviation and ground fuels. V,Ni, Fe, and Na are the major metallic constituents of crude oil that canpropagate down to the final refined fuel product. Other metals can beintroduced during production, transportation and storage, either indiluted or micro/nano-particulate forms. The real-time detection ofthese metals at a sub-ppm level is critical to ensure high quality ofdefense logistics fuels. An analytical technology that can be instantlyapplied anyplace on-site is key to the efficient fuel qualitysurveillance program. However, such analytical technology has notexisted before the present embodiments and methods.

Pulsed laser ablation does not introduce any risk of fuel ignitionbecause the fuel aerosol micro-droplets are instantly atomized and thereare no combustion reactions. Operation in a nitrogen flow avoid thepresence of any oxidant that can support combustion. Currently,commercial benchtop LIBS instruments designed for solid samples providedetection limits at levels of low to sub-ppm for most metals, and lowppb for some of them (comparable to ICP-OES). Ultrasonic nebulizers insome present embodiments are operable to produce an aerosolapproximately 10 times denser than conventional ICP nebulizers, they canaccordingly provide 10 times lower detection limits.

An ultrasonic nebulizer cannot be directly used to inject a dense liquidaerosol for analysis in ICP-OES or ICP-MS because the plasma would beextinguished by the very high sample load supplied by such nebulizers.Thus, a desolvation system would be required between the nebulizer andthe plasma to effectuate analysis in this matter. This is an inherentlimitation of an inductively coupled plasma source regardless of whetheran aqueous solution or organic material such as jet fuel is the subjectof analysis. By contrast the apparatus and methods of using instant LIBSfor analysis of liquid samples, does not suffer from this limitationbecause the LIBS laser directly excites emission via excitation andionization brought about by laser ablation.

Accordingly, LIBS in combination with ultrasonic nebulization functioncooperatively to provide a method of elemental liquid analysis that hasnot been possible with prior art methods and apparatus. An ultrasonicnebulizer can be based on using a crystal transducer to impart energyoperable to break up a liquid sample into fine droplets. The transducerwithout the desolvation apparatus can be miniaturized. It can be seenthat the disclosed combination of a nebulizer and LIBS will be operableto achieve at least sub-ppm to ppb level detection limits for mostmetals in a liquid medium. Moreover, an ultrasonic nebulizer having nodesolvator can retain even volatile elements (e.g. Hg), which wouldotherwise be depleted or totally lost during desolvator processing.

A series of tests using aqueous solutions and light solvents confirmedthat the LIBS apparatus embodiments were useful to analyze any liquidsample having low enough viscosity for direct nebulization.

Chemical analysis of jet fuel using instant LIBS with directnebulization is feasible. Owing to the fact that jet fuel is ordinarilyclean and free from large particles (>0.5 μm) and is neither toovolatile nor too viscous for direct nebulization. Similarly, theproperties of diesel fuel are also compatible with the directnebulization in combination with LIBS. Both fuels were easily convertedinto a dense aerosol using an ultrasonic nebulizer. This dense aerosolwas effectively excited by a LIBS laser thereby facilitatingultra-sensitive trace analysis.

Several low-viscosity nutrient liquid samples used in the food industrywere analyzed using the disclosed methods in an embodiment. Aninstrument configuration having a compact 6-channel spectrometer and CCDdetectors was used to perform rapid acquisition of broadband spectraemitted from a luminous LIBS plume. A multivariate partial least squaresregression was applied for quantitative calibration of the LIBS spectra.For comparison, concentrations of Mg in these samples was also measuredusing conventional ICP-OES. The results of LIBS and ICP-OES measurementsfrom 5 different samples of nutrient liquid are shown in FIG. 20 . Themeasured values of Mg concentrations by both techniques are in goodagreement.

An embodiment of the disclosed LIBS methods and apparatus combines andintegrates a liquid analysis module and a solid analysis module in oneinstrument. A software-controlled mechanism operable to move a mirrorwas used to switch the ablation laser beam between the modules, foranalysis of a liquid or solid sample as required. This design is modularand can be customized to satisfy various different needs andrequirements. Some end users may prefer a lower cost embodiment havingrelatively fewer functions. There are embodiments of the disclosedapparatus configured to be portable, yet they allow quantitativeanalysis of metals without compromising sensitivity at the low ppm orsub-ppm ranges.

Another aspect relates to the LIBS described herein includes thecapability to quantify the 3-dimensional (3D) elemental composition ofany solid phase samples in high spatial and temporal resolution. Solidsamples such as multilayered, coated, composite, granulated, other formsof structured materials and/or material structures can be mapped andprofiled chemically in x, y and z axes using LIBS. These types of 3Dchemical analyses are useful for new battery design structures, learninglithium-ion transfer cycling mechanisms, impurity detection, qualitycontrol, evaluation of distribution and structural changes due to agingof devices.

In some embodiments, the elemental composition of thin-film structuresfound in photovoltaic, electronic devices, and solar cell structures canbe analyzed using the 3D chemical imaging methods of LIBS to assessquality and/or state of a product. In another embodiment, instant LIBS3D mapping and profiling methods can be used to analyze the binder andconductive agent distributions, a critical parameter of a batteryperformance, in Li-ion batteries and/or similar types of batteries. Anyinhomogeneity in the binder and conductive agent distribution affectselectrical performance of a battery adversely and may cause reducedbattery performance.

3D elemental imaging can be essential for the analysis of spentcatalysts to inspect how and when contaminants attach to a catalystsurface in a battery. In some embodiments, 3D elemental distributions ofcatalyst materials in batteries can be measured using present LIBS 3Dchemical imaging apparatus and methods to assess the battery performanceas these catalyst materials are good indicators of the activity andperformance of a catalytic process. In some embodiments, 3D chemicalmapping of a catalyst surface and depth profiling overtime can be usefulto monitor to understand how contaminant elements adhere, bond andpenetrate into the catalyst volume. In further embodiments, the chemicalcharacterization of individual particles and grains of minerals providesinformation related to the composition, location of inclusions, mineralphases, and mineralogical distribution of elements. The disclosed LIBSinstrument and methods herein allow users to spatially analyze solidsamples for all major, minor, and trace elements including the lighter,organic, and halogen elements (e.g. H, Li, Be, B, C, O, N, F, and Cl)that are difficult or impossible to detect by conventional techniques.

Generally, a relatively high fraction of alumina and silica in typicalcatalyst materials used by petroleum refineries makes them difficult todissolve in acids or aqua regia as necessary for traditional ICPanalysis. Digestion of catalysts often requires hydrofluoric (HF) acid,which is dangerous, expensive and generates hazardous waste. Thechemical mapping of the catalyst surface and depth profiling areimportant for monitoring how the impurity metals (e.g. Al, Ni, Fe, V,Cu, and Ti) adhere, bond and penetrate into the catalyst volume. Areconstructed elemental image of a spent catalyst sample demonstratedsignificantly elevated concentrations of nickel at and close to thesurface. The concentration of Ni dropped with depth in a profile goinginto the bulk sample.

In an exemplary embodiment for 3D solid sample analysis of instant LIBS,each component in a cell in an Li-ion battery structure can be mappedand depth profiled to generate a 3D chemical imaging and to assess thequality of each component in a cell rapidly. FIG. 21A shows a typicalcell structure K10 in a Li-ion battery K50 and a 3D chemical analysisprocedure using instant LIBS. The cell structure K10 includes chemicallydistinct layers such as layer 1, layer 2, layer 3, and layer 4. A 3Dchemical image of a solid sample can be generated by repeating theprofiling procedure in a grid of preselected x and y map locations K70.Laser pulses are directed repeatedly into a preselected planarcoordinate location in x, y, z directions until a substrate and/or abottom of the analyzed structure is reached. Each laser pulse ablates aconsecutive volume of sample material K20, and thus penetrates deeperinto the sample structure. Each laser pulse generates an opticalspectrum that characterizes that portion of the sample ablated by asingle laser pulse. FIG. 21B shows the spectral intensitiescorresponding to layer 1, layer 2, layer 3, and layer 4 of cellstructure K10 in a Li-ion battery. The depth profiling resolution oflaser ablation was found to typically be in the range of 10 to 100 nmdepending on the sample material. Minimum lateral resolution cantypically be as low as 10 μm. Although in practice lateral resolution isoften more than 10 μm it also depends on sample material. Generally hardmaterials characteristically support the best spatial resolution. Depthprofiles can be performed on structures with more than 100 μm thicknesswith less than 1 μm depth resolution.

Also, measuring 3D chemical distributions can be useful for posterioranalysis of human biominerals, gallstones, kidney stones, bladderstones, sialoliths, teeth, fingernails, bones, malignant skin, and otherbiological tissues. The disclosed LIBS profiling apparatus and methodscan be also beneficial for microbiological, animal and plant studies,particularly for measuring distributions in contaminated or doped plantleaves. LIBS enables 3D elemental imaging at microscopic spatialresolution of entire organs especially after administering metal-basednanoparticles. The disclosed LIBS apparatus is important forenvironmental forensics, geological studies, analyzing drilling cores,shale exploration, and many other fields.

Another aspect for solid sample analysis provides a method of the 2D-and 3D-elemental imaging of individual minerals and mineralogicaldistribution of elements in geological samples. Practitioners in thefield will appreciate high sensitivity of LIBS to spatially analyzelighter elements with atomic numbers Z<10 (e.g. H, Li, Be, B, C, O, N,and F) that can be present in high abundance in natural minerals. Theseelements can be the main constituents of minerals, e.g. Li and F thatare often found in some micas. The lighter elements are missing from theanalysis by conventional techniques due to lack of sensitivity andfailure to detect. LIBS allows for in situ analysis of small mineralgrains and inclusions. The analysis of water or gas inclusions inminerals and rocks is also possible using LIBS.

In one embodiment for exemplary demonstration, LIBS can be used as ameans for detecting fluorine and oxygen in a mineral sample containingdistinct regions of bastnasite (carbo-fluoride) and barite (BaSO₄). Thesample was analyzed and the elemental composition over an area ofinterest was mapped using contour plots. FIG. 22A-C illustrate theresults of 2D elemental profile of the bastnasite-barite sample usinginstant LIBS. Low concentrations of elements are represented by whitecolor and higher concentrations are represented by darker shades inFIGS. 22B and 22C. 2D elemental imaging analysis of the mineral bypresent LIBS shows different 2D distribution patterns of fluorine (seeFIG. 22B) and oxygen (see FIG. 22C) in the mapped area of the mineralsample.

In another example of elemental mapping for ruby-in-zoisite gem rock,LIBS revealed the distribution of elements such as H, O, Li, K, Na, andMg that are difficult or impossible to detect using conventionaltechniques. Instant LIBS was effective in identifying main ruby andzoisite crystals as well as other constituent minerals within theanalyzed area. Spatially resolved chemical information provides valuableinsight on mineral phases present, location of inclusions, mineraldistribution of elements harmful to downstream product extraction, andoverall content of the target minerals. An embodiment of the disclosedLIBS apparatus allows geochemists to measure the content anddistribution of elements that remained elusive in the past. LIBSanalysis can improve decisions about processing mineral products.

The present disclosure also includes analysis of individual solidparticles on a substrate such as filter paper, swipes, or double-sidedadhesive tape. The advantage of the disclosure is that LIBS can measureelemental composition of the particles which are significantly smallerthan a laser spot size on the sample site. Analysis of particles withsub-micron sizes and sub-nanogram masses is possible according to anembodiment of instant LIBS apparatus. Using instant LIBS method,chemical analysis of toxic, radioactive, or other particles on specimensurfaces can be done easily. Furthermore, analysis of individual solidparticles embedded in ice or other matrices and/or detection andquantification of nanoparticles-based biomarkers and labels administeredto tissues are also feasible. Similarly, the sensitive analysis ofmicro-particles is necessary in forensics and safeguarding againstillicit manufacture of nuclear materials.

In an exemplary trial with a Peltier cooled chamber, polar ice-coresamples were analyzed for determining paleoclimate proxy indicators suchas particles containing Ca, K, Mg, Na, and other metals. Earlieranalysis of these ice samples by ICP-MS established average elementalconcentrations of parts-per-trillion (ppt). A LIBS embodimenteffectuated visual navigation through a magnified image of the icesamples to enact relevant movement of x-y-z stages to place a particleinto a spot where a laser beam would impinge. A single laser pulseobliterated the whole particle, revealing a spectrum and thereforecomposition of each individual particle. High spatial precision of LIBSallowed narrowing the age interval (<0.5 years) to see abruptpaleoclimate change events. Such high sensitivity is unattainable byICP-OES, XRF and/or similar techniques. Only average concentrations in appt range can be measured by ICP-MS. Other applications include rapidmetallurgical analysis and identification of individual debris particlescollected on filters from aviation fuel and/or used motor oil. Debrisalloy identification facilitates assessment of the degree of possibledamage in engine components.

Repeatability of the LIBS measurements was tested using aerosolizedsamples of organic solvents and mineral oil with 100 ppm vanadiumtraces. The relative standard deviation of the vanadium line intensitywas 1.45% over 12 sets of measurements with 20 accumulated spectra each.Experiments with bulk analysis of solid samples demonstrated that signalaveraging over multiple ablation pulses improves the precision ofmeasurements. Analysis by the disclosed LIBS apparatus of a thin glassyfilm deposited on silicon wafers that represent solid homogeneoussamples resulted in relative standard errors from 0.3 to 0.5% of theaverage LIBS intensity over 100 laser pulses. By contrast, inhomogeneousmineral samples of boron ore that were powdered, homogenized andpelletized were then analyzed by LIBS using 1360 laser pulsesaccumulated into 20 spectra per sample. A resulting average relativestandard deviation was 1.2% among 15 samples. These trials demonstratedthat the averaged LIBS measurements had acceptable precision even whenthe samples were inherently inhomogeneous. This is of particularimportance because a person having ordinary skill in the art wouldappreciate that boron is difficult to measure by other techniques.

An automated version of the LIBS instruments is developed for factoryshift workers or technicians with no experience performing LIBS analysisand/or quantitative chemistry. The “Axiom” software platform prompts thetechnician at every step of the data collection process, i.e., loadingthe samples, ensuring the sample focus, placing pre-loaded experimentalmethods in the proper locations, and saving the data. The data saved bythe user is processed by an automated version of the “Clarity” dataanalysis software. This automated software can create calibrationcurves, process unknowns for quantitative treatment, and export data inthe form of a tab-delimited text file. Qualitative data may also beexported in the form of depth profiles and map figures. The “Clarity”software platform can be programmed to perform traditional univariatecalibration via integration of predetermined elemental emission lines orto perform multivariate calibration via historical data libraries.

The operations of the disclosed apparatus and methods are executed usinga various software embedded in the instrument comprising advancedchemometric algorithms, multivariate regression models, and dataacquisition. All data is acquired by the Axiom platform and isautomatically uploaded into “Clarity”. The Clarity data analysissoftware offers a full suite of data analysis tools for rapid processingof LIBS spectra. The software provides rapid analysis of large arrays ofspatially-resolved LIBS data (e.g. 2D and 3D chemical imaging data). Thedepth profiling for 3D chemical imaging is facilitated by a real-timeDepthTracker module. In various embodiments, background subtraction,signal smoothing; normalizing; averaging, obtaining intensities andstandard deviations are also operable functions of this embeddedsoftware. This software also provides automatic identification ofspectral lines, integration of their peak areas either directly or usingLorentzian and Gaussian fitting of the line contours, and deconvolvingpartially overlapped spectral line contours. The software also comprisesan algorithm operable to predict spectral peak intensities and plasmatemperature based on a local thermodynamic equilibrium (LTE) plasmamodel. Calibration can be performed using techniques based on univariateand multivariate regression models, in single or in combination.Relevant spectral reference databases can be custom-built using areference library creator module.

The software can also be programmed to upload the results to a databaseautomatically. This technology allows a sophisticated chemical analysisto be performed by shift workers in a factory setting withoutsupervision. These advances facilitate fast analysis of solid sampleswith full automation of the data collection, reduction (based on acombination of univariate and multivariate models) and reporting thatenables quick decision about production and processing of materials.

The majority of the software functions are designed for analysis ofsolid samples. A special part of the operating software is dedicated tothe analysis of liquid samples. The “Clarity” data analysis software iscommon for both liquid and solid samples.

In the foregoing specification, various aspects are described withreference to specific embodiments, but those skilled in the art willrecognize that further aspects are not limited thereto. Various featuresand aspects described above may be used individually or jointly. Otheraspects of the invention, including alternatives, modifications,permutations and equivalents of the embodiments described herein, willbe apparent to those skilled in the art from consideration of thespecification, study of the drawings, and practice of the variousaspects. Further, various aspects can be utilized in any number ofenvironments and applications beyond those described herein withoutdeparting from the broader spirit and scope of the description. Thewritten description and accompanying drawings are, accordingly, to beregarded as illustrative rather than restrictive.

Although various embodiments have been presented and explained usingsimplified examples, it will be understood that various changes andmodifications are possible with regard to materials, shapes, anddimensions, without departure from the scope of the patent claims. Theembodiments and preferred features described above should be consideredexemplary, with the invention being defined by the appended claims,which therefore include all such alternatives, modifications,permutations and equivalents as fall within the true spirit and scope ofthe present disclosure.

What is claimed is:
 1. An apparatus for ablation spectroscopy,comprising: a pulsed laser configured to ablate material from a sampleinto an emissive plasma plume with a laser pulse; a plurality ofspectrometers, each having a wavelength separating element and adetector; and a branched fiber optic lightguide having an entire bundleof optical fibers in a trunk section of the fiber optic lightguideadjoining a light receiving end of the trunk configured to collect lightoriginating from the emissive plasma plume, the entire bundle of opticalfibers in the trunk section being subdivided into a plurality ofbranches, each branch comprising a respective exclusive subset of theentire bundle of optical fibers, whereby each optical fiber in theexclusive subset of the entire bundle in a branch runs from the lightreceiving trunk end of the branched fiber optic lightguide to a terminalend of said branch; wherein: a terminal end of a first branch of abranched fiber optic lightguide is configured to emit a first portion ofthe collected light into a first spectrometer, and a terminal end of asecond branch of the branched fiber optic lightguide is configured toemit a second portion of the collected light into a second spectrometer;and the computer is configured to receive spectral data comprising firstspectral data from the first spectrometer and second spectral data fromthe second spectrometer, and the computer includes tangible mediacomprising instructions and data operable to determine a representationof the sample composition based on the spectral data.
 2. The apparatusof claim 1 wherein each of the optical fibers in the entire bundle ofoptical fibers in the trunk section of the branched fiber opticlightguide has a same diameter.
 3. The apparatus of claim 2 wherein thenumber of optical fibers in the first branch of the branched fiber opticlightguide is larger than the number of optical fibers in the secondbranch of the branched fiber optic lightguide whereby the emitted firstportion of the collected light is greater than the emitted secondportion of the collected light.
 4. The apparatus of claim 1 furthercomprising an unbranched fiber optic lightguide having two endsconsisting of a light receiving end configured to collect lightoriginating from the emissive plasma plume and a terminal end configuredto emit collected light into a third spectrometer, wherein an entirebundle of optical fibers runs from the light receiving end of theunbranched fiber optic lightguide to the terminal end of the unbranchedfiber optic lightguide, and the spectral data received by the computerfurther comprises spectral data from the third spectrometer.
 5. Theapparatus of claim 4 wherein each optical fiber within the unbranchedand the branched optical fiber lightguides has an equal diameter.
 6. Theapparatus of claim 5 wherein the radiant flux of light emitted from theterminal end of the unbranched fiber optic lightguide is greater thanthe radiant flux of light emitted from the terminal end of the firstbranch or the radiant flux of light emitted from terminal end of thesecond branch of the branched fiber optic lightguide.
 7. The apparatusof claim 4 wherein the third spectrometer has a Czerny-Turner wavelengthseparating element.
 8. The apparatus of claim 4 wherein the thirdspectrometer has a Czerny-Turner wavelength separating element and anICCD detector.
 9. The apparatus of claim 4 wherein the thirdspectrometer has a higher resolution and narrower spectral range thanany other spectrometer selected from among the plurality ofspectrometers.
 10. The apparatus of claim 4 wherein the firstspectrometer is a relatively broadband spectrometer and the secondspectrometer is a relatively narrowband spectrometer.
 11. The apparatusof claim 4 wherein the first spectrometer has a detector selected fromthe group consisting of a CMOS detector and a CCD detector.
 12. Theapparatus of claim 11 wherein the second spectrometer has aCzerny-Turner wavelength separating element.
 13. The apparatus of claim12 wherein the second spectrometer has an ICCD detector.
 14. Theapparatus of claim 4 comprising an array of spectrometers havingrespective Czerny-Turner wavelength separating elements, wherein eachspectrometer of the array is configured to cover a different preselectedwavelength region and the array of spectrometers is configured tocapture a broad range of wavelengths at one time.
 15. The apparatus ofclaim 4 further comprising: an inductively coupled plasma massspectrometer operable to determine ion mass to charge ratios and ionmass to charge peak intensity values from a portion of the ablatedsample site material; an enclosure configured to enclose the sampleduring the pulsed laser ablation; a flow channel connecting theenclosure to an inductively coupled mass spectrometer; and a gas flowsystem configured to provide a flow of unreactive carrier gas to theenclosure wherein the portion of the laser pulse ablated sample sitematerial is transported through the flow channel to the inductivelycoupled mass spectrometer; wherein the computer is further configured toreceive the ion mass to charge ratio peak intensity values from theinductively coupled plasma mass spectrometer, and the tangible mediacomprises instructions and data operable to determine the selectedsample site composition based on the spectral data and the normalizedion mass to charge ratio peak intensity values.
 16. The apparatus ofclaim 15 wherein the data and instructions are operable for the computerto detect a pulse-to-pulse variation in an amount of material ablatedfrom a selected sample site by a laser pulse based on a signal levelobtained from the spectral data; normalize ion mass to charge ratio peakintensity values for the pulse-to-pulse variation in the amount ofmaterial ablated from the sample using the signal level; and determinethe selected sample site composition based on the spectral data and thenormalized ion mass to charge ratio peak intensity values.